Background Internet sex-seeking has been associated at the person level with sexual risk. However, the most robust method of encounter-level inference to determine associations between internet sex-seeking and sexual risk is to compare encounters against each other. We systematically reviewed within-subjects comparisons of sexual encounters that tested associations between internet sex-seeking and sexual risk in men who have sex with men. Methods: We systematically searched databases on 9 July 2013, then screened records and full-text articles in duplicate and independently. Studies were synthesised narratively. Results: Four studies were included. Although studies were generally of high quality, the findings were inconsistent and did not show clear evidence of a relationship between internet sex-seeking and sexual risk. Conclusions: Further research in internet sex-seeking among men who have sex with men is required, particularly as internet-enabled sexual sociality continues to evolve. Internet-based health promotion may wish to target person-level features instead of encounter-specific characteristics.