STUDY QUESTION: What are the demographic characteristics, motivations, preferences and experiences of heterosexual, gay and bisexual sperm donors on a connection website (i.e. a website that facilitates direct contact between donors and recipients of gametes)? SUMMARY ANSWER: This demographically diverse group of men was donating for altruistic reasons and perceived the website as providing greater choice over donation arrangements: approximately one third favoured anonymous donation, most of whom were heterosexual, whilst gay and bisexual donors were more likely to be in contact with children conceived with their sperm. WHAT IS KNOWN ALREADY: Despite substantially more sperm donors being registered on connection websites than with clinics, there has been very little research on this population. Current understanding of the impact of sexual orientation on donors' attitudes is also limited. STUDY DESIGN, SIZE, DURATION: An online survey was conducted over 7 weeks with 383 men registered as sperm donors with Pride Angel, a large UK-based connection website for donors and recipients of sperm. PARTICIPANTS/MATERIALS, SETTING, METHODS: The survey obtained data on participants' demographic characteristics and their motivations, preferences and experiences regarding online sperm donation, including attitudes towards contact with offspring. Differences according to participants' sexual orientation were examined. MAIN RESULTS AND THE ROLE OF CHANCE: Most participants (80.4%, 308) were heterosexual, 10.5% (40) were gay and 9.1% (35) were bisexual; ages ranged from 18 to 69 years (median = 36, mean = 37.3, SD = 9.7). A greater proportion of gay and bisexual men desired open-identity donation (P < 0.005) and contact with offspring (P <0.005) than heterosexual men. Approximately one third (28.7%, 110) had donated sperm; 18.3% (70) had conceived at least one child, of whom a minority (25.7%, 18) were currently in contact with the child, comprising significantly more gay and bisexual than heterosexual men (P = 0.001). Heterosexual men were most likely to state a preference for natural insemination, although the large majority (94.3%, 66) of donors who had conceived children had used artificial insemination. LIMITATIONS, REASONS FOR CAUTION: Findings may not be representative of all sperm donors using connection websites because members of only one website participated and participants were, by necessity, a self-selected sample. WIDER IMPLICATIONS OF THE FINDINGS: This is the first comprehensive study of donors who connect with recipients via the internet, including a substantial number who have donated and conceived children. The findings indicate that sexual orientation may influence men's donation preferences and raise policy issues concerning donor recruitment and the incorporation of online sperm donation into clinical practice. STUDY FUNDING/COMPETING INTERESTS: This study was supported by the Wellcome Trust (097857/Z/11/Z). E.T. is the co-founder of Pride Angel; the remaining authors have no conflicts of interest.