Abstract Background: The increase in the numbers of (gay) backrooms and saunas in London has generated anxieties about gay male promiscuity and the consequent transmission of STIs including HIV. In order to assess risk, we conducted a qualitative study investigating the circumstances under which men engaged in anal intercourse (AI) and unprotected anal intercourse (UAI) in these venues and the risk reduction strategies used. Methods: 20 men were recruited at backrooms and saunas for individual in -depth interviews covering sexual and practical motivations for anonymous sex, detailed accounts of sexual negotiation and behaviour and perceptions of risk. Interviews were audio tape-recorded and transcribed. A case by case analysis of transcripts was followed by a thematic content analysis. Results: The majority of accounts of AI and UAI in backrooms and saunas were characterised by total anonymity. The eroticism associated with anonymity facilitated a range of erotic, transgressive or fetishistic desires and sexual role play (such as sado-masochistic or dress -code scenes). Partners were imbued with imaginary hyper sexual or hyper masculine attributes and fantasies were therefore personal to the individual engaging in them and not necessarily shared by his partner. Risk reduction strategies were informed by knowledge or assumptions about one’s own and one’s partner’s HIV status as well as assessments about the likelihood of HIV transmission during UAI (for example, that HIV transmission is less likely if the infected partner is receptive). Personal narratives of risk taking were identified which were psychologically, socially and morally protective for the individual. These narratives depended on beliefs and assumptions as well as the positing of an ‘ideal’ UAI partner. Discussion: Anonymous UAI was not due to a lack of care (for the self or one's partner), diminution of judgement (being 'carried away' or intoxicated), or denial (either of the presence of HIV or of it’s severity). Many men who use backrooms and saunas are used to developing strategies and taking calculated risks. Although men’s strategies and decisions around avoiding HIV transmission will be personal and nuanced, it is possible to identify a general logic that is applied in many accounts of UAI in backrooms and saunas.