This study compared respondents who completed an Internet sexuality questionnaire and those who dropped out before completion. The study was in Swedish and comprised 3,614 respondents over a 2‐week period (53% males, 47% females). There were significant differences between males, of whom 51% dropped out before completion of the 175‐item questionnaire, and females, of whom 43% dropped out. Dropout in both genders followed a curve of negative acceleration. The data suggest that dropout is likely to be significant and gender and demographically biased, and to occur significantly earlier for men than for women. Geography, education, sexual orientation, age, relationship status, living arrangements, and Internet connection speed were related to dropout for men, while only relationship status and living arrangements, which were in the opposite direction from men, were related to dropout in women.