Diabetes mellitus (DM) is increasing worldwide and places a substantial burden on health systems through its complications. Background/Objectives: To identify factors associated with DM-related complications in adults receiving primary care in Rio Branco, Acre, western Brazilian Amazon. Methods: Population-based cross-sectional study in 30 Family Health Strategy (FHS) units; 324 participants, weighted to represent 2,245 adults with DM. Five binary outcomes were analyzed: self-reported stroke, electrocardiographic (ECG) abnormalities, microangiopathy, chronic nephropathy, and any complication. Associations were estimated by Poisson regression with robust variance. Results: About 72% of participants had at least one complication. Any complication was independently associated with male sex (PR = 1.23), age ≥ 60 years (PR = 1.25), hypertension (PR = 1.34), illiteracy (PR = 1.18) and ≤ 3 medical appointments in the previous 12 months (PR = 1.46). Distinct factors emerged for each individual outcome. Conclusions: DM complications were highly prevalent and driven by multifactorial determinants, supporting risk stratification, early detection and targeted interventions in primary care.