In a prospective study of 189 colorectal operations, the subcutaneous fat layer in the abdominal incisional wound was measured for correlation with wound infection. The infection rate was 20% when the fat layer was greater than or equal to 3.5 cm and 6.8% when the thickness was less than or equal to 3 cm (statistically significant difference). This c. threefold rise indicates that in obese patients special attention should be directed to antibiotic and other prophylaxis against incisional infection.