Monkeypox is a zoonotic disease and leads to a smallpox-like disease in humans. The current epidemic in European countries requires informed responses. We investigated the ability to self-diagnose a potential infection, and determinants of vaccination and self-isolation intention after diagnosis among 394 MSM in the Netherlands. We found that about half were able to self-diagnose monkeypox, that 70% had a high intention to get vaccinated and 44% to self-isolate after monkeypox diagnosis. Determinants went beyond mere risk behaviour criteria.