BACKGROUND: Obesity is at epidemic proportions. This study examined the extent to which obesity is being diagnosed at a community health center residency-training site. Results were examined by provider type. Characteristics of patients with obesity diagnosed by primary care providers were compared with characteristics of patients determined to be obese by body mass index (BMI) calculation exclusively. METHODS: A cross-sectional design was used. Medical records of 465 adult patients were audited. Data collected included diagnosis of obesity, height and weight, demographics, and comorbidity. RESULTS: Of the 465 patients' charts audited, 83 contained a provider diagnosis of obesity, and 74 additional patients were determined to be obese by BMI calculation exclusively. Significant underdiagnosis occurred among all provider types (P = .036). Patients with a diagnosis of obesity had significantly higher BMI scores (38.4 vs 34.4, P = .002). Obesity was more likely to be diagnosed in female than in male patients (P = .001). Differences related to age, insurance coverage, and comorbidity were not significant. CONCLUSIONS: Obesity was found to be an underdiagnosed condition among all provider types. As evidenced by significantly higher BMI scores for provider-diagnosed obesity, the data suggest that the obesity diagnosis is made by appearance. The importance of teaching and modeling the use of BMI to diagnose obesity is underscored.