There have been some issues censored by customs. I'm not referring to Heavy Metal placing word bubbles over certain things, but actually customs ripping out pages, or blacking out certain things when shipping to other countries. The most known censored issue is Spring 1988, which because of Canadian "sex with violence" import laws, 36,000 copies had the Druuna story censored. It also had an explanation note stuck to its contents page. The next issue, Summer, also had an editorial about the situation. Another issue that was censored was November 1997, which had one page torn out of the Gypsy story in thousands of issues. For a while, HM offered people an exchange for an uncensored copy for a small fee. September 1995 was another issue that was censored because of the Druuna story. However, it usually doesn't get censored country wide, and only a few copies get censored, depending on where the issue is going, what customs want to do with it, and what distributors want to do with it. There have been many other issues that have been censored.

Before 2013, there were only four issues that had a variant cover. November 1999, has a limited edition with the cover by Frank Miller to benefit the Comic Book Legal Defense Fund. September 2008, has a limited edition with the cover by Nathan Fox made for the Fluorescent Black story within and given out at the 2008 San Diego Comic-Con. September 2011, has a limited edition with the cover by Artgerm and was given out at the 2011 San Diego Comic-Con. May 2012 was the 35th anniversary issue, and reused the same illustration from the first issue, along with 3 similar variants. From 2013 onward, variants would become common with nearly every issue.

There are a few issues that have used the same cover illustration. The Best Of special used the same illustration as the June 1977 issue. January 2002 used the same illustration as the Summer 1988 issue. May 2012 used the same illustration as the April 1977 issue. And #314 used the same illustration as the February 1982 issue.

For the Special issue, "Heavy Metal's Even Heavier Metal", there's no one credited for the cover illustration. Lost in time it seems no one remembers who it was.

The Special issue, "War Machine", is the only issue to have a 3 page fold out cover.

Heavy Metal doesn't reprint stories that have already been printed in previous issues. However, there are a few exceptions, such as the issues The Best Of, The Best Of #2, 15 Years Of, Greatest Hits, and One Step Beyond. Also the story Bird Dust in January 1984 was previously printed in November 1977. And the story The Bus was printed in January 1985 and again in July 1985. And the story A Mudwog Tale was printed in May 1981 and again in September 2005. And in March 1990, there was a story for The Incal, which in July 1995 was remade with a different artist for the Meta-Barons story. And in June 1978, there was the feature, Galactic Geographic, which was later reprinted as a rewritten and expanded version in the Spring 1998 issue. And in March 1993, there was the start of the Melting Pot story, which was later reprinted in full as a remade and expanded version in the Fall 2007 issue.

There have been many different kinds of mailing covers and bags over the years. These all vary depending on if they're subscriptions, or store bought, or where they were sent. If it's in a store, a bag can prevent minors from flipping through the issue. Bags can also censor the cover, if needed to get past customs. Unfortunately, the process to seal these bags can also cause the ink to come off where the seams are. Both bags and mailing covers can be great to stick the mailing label to, instead of ruining the actual cover. Although with some issues, mainly early ones, mailing labels have been stuck to the magazine cover. The December 1985 mailing cover had a note on it, telling subscribers about the frequency change from monthly to quarterly.

On the cover of early issues, there was the standard UPC box with the bar code for being scanned in stores. But not all copies had this. The first issue, April 1977 doesn't have that box at all, and January 1978 has "Les Humanoides Associes" in its place. Excluding January 1978, every issue from June 1977 to March 1981, has either a bar code if it was sold in stores, or "Les Humanoides Associes" if it was a subscription. Then every issue from April 1981 to Winter 1987, has either a bar code if it's from a store, or "HM" if it was a subscription.

A special 1986 issue of the French Métal Hurlant was double numbered 121 and 122.

In the April 1982 issue of Epic Illustrated it was advertised as their "Third Anniversary" issue. Even though it was the start of their third year, they were only two years old at this point, so it should actually be their "Second Anniversary" issue.

Tanino Liberatore illustrated the album cover for Frank Zappa's "The Man From Utopia". It shows Frank as Ranxerox. There is also a similar illustration on the back cover.

The illustration for National Lampoon's Vacation (1983) by Boris Vallejo was a parody of the Den illustration.