Backgrounds The incidence of diabetes mellitus (DM) in people living with human immunodeficiency virus (HIV) receiving highly active antiretroviral therapy (HAART) is thought to be higher than that in noninfected people. The aim of this study was to investigate the prevalence of DM among people living with HIV in Dammam, Saudi Arabia (SA). Methods This was a cross-sectional study that included adult patients with HIV who were followed at Dammam Medical Complex. The electronic medical records of the patients were reviewed for their demographic data, comorbid conditions, and HIV history (e.g., duration and medications). The patients were categorized based on their glycated hemoglobin (A1C) levels into nondiabetic patients (A1C < 5.7%), prediabetic patients (A1C between 5.7% and 6.4%), and diabetic patients (A1C ≥ 6.5). Results A total of 769 HIV patients were assessed. The A1C of 325 patients could not be retrieved. The remaining 444 patients were included in the analysis. These consisted of 71 female patients (15.99%) and 373 male patients (84.01%). The average age of the patients was 38.62±11.33 years. Their duration for living with HIV was on average 3.76±3.15 years. The cohort consisted of 290 nondiabetic patients (65.32%), 107 prediabetic patients (24.1%), and 47 diabetic patients (10.59%). The nondiabetic patients were generally younger than the prediabetic patients (35.97 vs 40.72 years on average, P value < 0.001). They were infected with HIV for shorter durations (3.45 vs 4.19 years on average, P value < 0.05) with a higher percentage of patients receiving antiretroviral therapy (97.93% vs 84.11%, P value < 0.001). Similarly, the nondiabetic patients were generally younger than the diabetic patients (35.97 vs 50.19 years on average, P value < 0.001). They were also infected with HIV for shorter durations (3.45 vs 4.65 years on average, P value < 0.05) with, also, a higher percentage of patients receiving antiretroviral therapy (97.93% vs 89.36%, P value < 0.01). Conclusions The prevalence of DM among people living with HIV in Dammam, SA, was high with DM remaining highly underdiagnosed in this population. However, the prevalence of DM in this study involving mostly HIV patients treated with newer HAART agents was lower than what was reported in multiple previous studies that included patients using older agents.