We examined the relationship between food insufficiency and antiretroviral therapy (ART) adherence. A cohort of HIV-infected adults in urban Peru was followed for a two-year period after ART initiation. ART adherence was measured using a 30-day self-report tool and classified as suboptimal if <95% adherence was reported. We conducted a repeated measures cohort analysis to examine whether food insufficiency was more common during months of suboptimal adherence relative to months with optimal adherence. 1,264 adherence interviews were conducted for 134 individuals. Participants who reported food insufficiency in the month prior to interview were more likely to experience suboptimal adherence than those who did not (odds ratio [O.R.]:2.4; 95% confidence interval [C.I.]:1.4, 4.1), even after adjusting for baseline social support score (O.R. per 5 point increase:0.91; C.I.:[0.85, 0.98]) and good baseline adherence self-efficacy (O.R.:0.25; C.I.:[0.09, 0.69]). Interventions that ensure food security for HIV-infected individuals may help sustain high levels of adherence.