Incels (involuntary celibates) base their identity on the inability to form romantic relationships. We conceptualize the ideology promoted by incels as misogynist extremism and explore the impact of the first COVID-19 lockdown on the radicalization of this online community. Based on computational measures, we conducted a multi-perspective exploration, comparing the prevalence of and participation in threads dealing with extremism, ideology and mental health on the incels.is forum between pre-lockdown, lockdown and post-lockdown periods. We found evidence of long-term and temporary radicalization. Moreover, we found that, specifically, older forum members increasingly post in extremist-themed threads triggered by the lockdowns. Crucially, we show that activity on mental health–themed threads temporarily decreased during the lockdown. These findings indicate that real-world social isolation reduces mental health complaints among incels but, at the same time, exacerbates misogynist extremism among active community members.