Irregular participation in HIV medical care hinders HIV RNA suppression and impacts health among people living with HIV. Cluster analysis of clinical data from 1,748 patients attending a large academic medical center yielded three HIV service usage patterns, namely: 'engaged in care', 'sporadic care', and 'frequent use'. Patients 'engaged in care' exhibited most consistent retention (on average, >88 % of each patient's observation years had ≥2 visits 90 days apart), annualized visit use (2.9 mean visits/year) and viral suppression (>73 % HIV RNA tests <400 c/mL). Patients in 'sporadic care' demonstrated lower retention (46-52 %), visit use (1.7 visits/year) and viral suppression (56 % <400 c/mL). Patients with 'frequent use' (5.2 visits/year) had more inpatient and emergency visits. Female, out-of-state residence, low attendance during the first observation year and detectable first-observed HIV RNA were early predictors of subsequent service usage. Patients 'engaged in care' were more likely to have HIV RNA <400 than those receiving sporadic care. Results confirm earlier findings that under-utilization of services predicts poorer viral suppression and health outcomes and support recommendations for 2-3 visits/year.