We analyzed results from the medical examinations of 340 hazardous materials (HAZMAT) firefighters and observed the relationships between selected parameters and body mass index (BMI). Heights and weights were available for 98% of the subjects (333 of 340). The mean BMI was 28.9 +/- 4.1 kg/m2. Eighty-seven percent (290 of 333) of subjects were overweight (BMI > or = 25) and 34% (113 of 333) were obese (BMI > or = 30). Two percent (7 of 333) were morbidly obese (BMI > or = 39). For comparison purposes, we divided subjects into low (BMI < 27), medium (BMI 27 to < 30), and high (BMI > or = 30) BMI groups. The results demonstrated adverse associations between increasing BMI and resting blood pressures, forced vital capacity, alanine aminotransferase, aspartate aminotransferase, serum cholesterol, and overall morbidity scores. The high prevalence of overweight and obesity and the associated adverse health effects support the development and implementation of fitness-promotion programs for firefighters.