Size variation of the bean leaf beetle (BLB),Cerotoma trifurcata(Forster), was evaluated, using adults from soybean fields in the Piedmont and Coastal Plain regions of North Carolina. BLBs sampled from the Coastal Plain counties, Currituck and Tyrrell, were largest. Within fields, late-season beetles were larger than beetles from earlier generations. Female BLBs were consistently larger than males in all samples. Multiple-regression techniques indicated that a small but significant amount of beetle size variation could be explained by eight field-related variables: field size, planting date, rainfall, row width, and percent sand, silt, clay, and organic matter in the soil. The magnitude of variation explained and relative importance of the variables differed between the sexes. Eight variables explained only 27 and 45% of variance in female and male size, respectively. The effects of soil moisture, texture, and temperature on adult size (weight) were determined under controlled conditions. In comparisons made among loamy sand, sandy clay loam, and organic soils, adult size was greatest in wet, organic soil and least in dry, loamy sand.