Background Testing for presence of HIV infection is a pre-requisite to qualify for antiretroviral treatment. A considerable proportion of German men who have sex with men (MSM) infected with HIV have a CD4 cell count below 350 cells/μl at time of diagnosis and are thus defined as “late presenters”. Late presentation increases the risk of adverse disease outcomes. In addition, knowledge and assessment of HIV status is often used for decisions about condom use and anal intercourse with steady and non-steady partners. Incorrect assumptions may result in high risk for HIV transmission. Methods Between 11/2013 and 01/2014 MSM were recruited to an online survey predominantly by personalized invitation messages from MSM social networking and dating websites. Respondents were asked about demographic characteristics, HIV testing history, reasons for testing decisions, and sexual behaviours. We describe reasons for not testing and analyse factors associated with not or infrequent testing using univariable and multivariable multinomial regression. Results Questions on HIV testing history were answered by 15,297 respondents. An HIV test within the last 12 months was reported by 38 %, a test more than 12 months ago by 27 % and 35 % had never been tested for HIV. Compared to recently tested, respondents who had never tested were more likely to be younger than 25 years (adjusted relative risk ratio (aRRR) 2.90, 95 % CI 2.11-3.99), living in a settlement with less than 100,000 inhabitants (aRRR 1.47, 95 % CI 1.18-1.83), being less open about their sexual orientation to their co-workers/classmates, and particularly to their primary care provider (aRRR 4.54, 95 % CI 4.02-5.11). Untested and less frequently tested respondents reported less sex partners and a lower proportion reported unprotected anal intercourse (UAI) with a non-steady partner (24 % compared to 38 % among those recently tested). Conclusions MSM who were younger, who did not live in large cities, and who were not out about their sexual orientation tested less frequently for HIV. Apart from strengthening protection from sexual orientation-related discrimination and empowering MSM who conceal their orientation, more opportunities to test anonymously and without revealing one’s sexual orientation should be provided.