We studied the association of once-daily dosing with self-reported adherence among participants of the Ontario Cohort Study who were currently taking ART and who had completed a 90-min interviewer-administered questionnaire. Suboptimal adherence was defined as missing ≥1 dose of ART in the 4 days prior to the interview. Participants (n = 779) were 85% male, 69% men having sex with men, 67% white, median age 48 years (IQR 42-54), median years of ART 9 (IQR 5-13) and median CD4 count 463 cells/mm(3) (IQR 320-638). Fifteen percent of participants reported suboptimal adherence in the 4 days prior to the interview. In a multivariable logistic regression model, participants on once daily regimens were half as likely to miss a dose during the 4 days prior to the interview. Other independent correlates of suboptimal adherence were younger age, lower positive social interaction and increased frequency of consuming > 6 alcoholic drinks on one occasion.