Thirty-day readmission rates, a widely utilized quality metric, are high among HIV-infected individuals. However, it is unknown how many 30-day readmissions are preventable, especially in HIV patients, who have been excluded from prior potentially preventable readmission analyses. We used electronic medical records to identify all readmissions within 30 days of discharge among HIV patients hospitalized at a large urban safety net hospital in 2011. Two independent reviewers assessed whether readmissions were potentially preventable using both published criteria and detailed chart review, how readmissions might have been prevented, and the phase of care deemed suboptimal (inpatient care, discharge planning, post-discharge). Of 1137 index admissions, 213 (19%) resulted in 30-day readmissions. These admissions occurred among 930 unique HIV patients, with 130 individuals (14%) experiencing 30-day readmissions. Of these 130, about half were determined to be potentially preventable using published criteria (53%) or implicit chart review (48%). Not taking antiretroviral therapy (ART) greatly increased the odds of a preventable readmission (OR 5.9, CI:2.4-14.8). Most of the preventable causes of readmission were attributed to suboptimal care during the index hospitalization. Half of 30-day readmission in HIV patients are potentially preventable. Increased focus on early ART initiation, adherence counseling, management of chronic conditions, and appropriate timing of discharge may help reduce readmissions in this vulnerable population.