Retention is a central component of the Cascade, facilitating monitoring of comorbidity. Country-specific definitions differ and may suit stable and functioning clients, while not appropriately classifying complex clinical presentations characterized by comorbidity. A retrospective file review of 363 people living with HIV attending a Sydney HIV clinic was conducted. Retention was compared with Australian (attendance once/12-months) and World Health Organization (attendance 'appropriate to need') recommendations to identify those attending according to the Australian definition, but not clinician recommendations (AUnotWHO). Multivariable logistic regression analyses determined the impact of age/sex and clinician-assessed comorbidity on retention. Most (97%) participants were considered retained according to the Australian definition, but only 56.7% according to clinician recommendations. Those with psychosocial comorbidity alone were less likely to be in the AUnotWHO group (OR 0.51, 95%CI 0.27-0.96, p = 0.04). The interaction of physical and psychosocial comorbidity was predictive of poor retention (Wald test: χ2 = 6.39, OR 2.39 [95% CI 1.15-4.97], p = 0.01), suggesting a syndemic relationship.