Internationally, gay men have been found to be at a higher risk of mental health problems than heterosexual men. However, there is little information about the mental health situation of Iranian gay men, a population facing serious legal repercussions. Additionally, there is limited international data on the effect of the COVID-19 pandemic on the mental health of gay men. The aim of this study was to evaluate Iranian gay men's mental health during this pandemic. We assessed depression, anxiety, and stress with the DASS and insomnia with the ISI in N = 176 Iranian gay men. We compared their DASS subscores with those of the general male population during the COVID-19 pandemic. 65.9% of Iranian gay men showed mild to extremely severe depression symptoms, 63.6% reported mild to extremely severe anxiety symptoms, 65.3% had mild to extremely severe stress symptoms, and 43.3% had mild to severe insomnia symptoms. Compared to the general Iranian male population, gay men reported significantly more depressive, anxiety, and stress symptoms. Iranian gay men show a high number of depression, anxiety, stress, and insomnia symptoms during the COVID-19 pandemic. Gay men reported significantly more mental health symptoms in the DASS subscores than the general population of Iranian men recruited during the pandemic. They showed descriptively more insomnia symptoms than Iranian adults before the pandemic. The mental health of Iranian gay men should be improved by abolishing punishments for same-sex sexual activities and establishing specialized mental health units for this population.