A prospective study was performed between April 1, 1991 and April 30, 1992 to determine factors involved in the development of post-Caesarean section wound infection. During this period there were 4,857 deliveries, 428 by Caesarean section (8.8%). Complete data were available on 328 (76.6%) patients. Wound infection occurred in 25.3% of women and was confirmed by positive bacteriology in 77.1%; 36% of wound infections were diagnosed following the patients' discharge from hospital. A negative correlation was found between maternal age and development of wound infection up to age 40 (p = 0.03). Maternal weight was a highly significant indicator of subsequent wound infection development (p = 0.0001), the relationship between increasing maternal weight and infection appearing linear. Antibiotic prophylaxis was found to be the most significant protective factor (p = 0.0007) in the reduction of postoperative wound infection. This relationship was independent of maternal weight.