Middle subcutaneous adipose tissue samples were excised dorsal to the first rib, lat rib, and last lumbar vertebrae of lean and obese swine (Yorkshire and Ossabaw gilts) one year of age. Average backfat thickness per 100 kg body weight was approximately five fold greater for obese swine (6.8 versus 1.5 cm, respectively). Adipocyte diameter and volume distributions were determined after fixation with OsO4 with a Coulter Counter. To preclude connective tissue debris contribution to adipocyte number determinations, 8 M urea was used to solubilize connective tissue. Within a breed among tissue sites no differences in adipocyte size distributions were observed. Adipocyte diameter distributions for first rib, last rib, and last lumbar were significantly biphasic for lean and obese swine. However, the diameter distributions were markedly different between lean and obese swine. Twice as many small cells (20-30 micrometer diameter) were present in distributions from obese swine. Maximum cell diameter for lean and obese swine was 140 and 190 micrometer, respectively. The appearance of biphasic diameter distributions in lean and obese swine one year old suggests that adipocyte hyperplasia is continuing long after the time earlier work had suggested that hyperplasia had ceased.