We have examined the expression and activity of 20-hydroxysteroid dehydrogenase (20-HSD) in abdominal adipose tissue in women. This recently-characterized enzyme from the aldoketoreductase 1C family (AKR1C1) is responsible for the conversion of progesterone into 20-hydroxyprogesterone. Abdominal sc (SC) and omental (OM) adipose tissue biopsies were obtained from a sample of 32 women aged 47.7 ± 5.9 yr (BMI: 27.6 ± 5.0 kg/m²) undergoing abdominal hysterectomies. Body composition and body fat distribution measurements were performed before the surgery by dual energy x-ray absorptiometry and computed tomography respectively. The expression of 20-HSD was determined by real-time RT-PCR, and its activity was measured in whole tissue homogenates. Messenger RNA and activity of the enzyme were detected in both the SC and OM fat depots, the two measures being significantly higher in the SC compartment. Women characterized by a visceral adipose tissue area greater than or equal to 100 cm² had an increased 20-HSD conversion rate in their omental adipose tissue compared with women without visceral obesity (13.99 ± 2.07 vs. 7.92 ± 0.83 fmol/µG protein/24 h, P < 0.05). Accordingly, a positive correlation was found between omental adipose tissue 20-HSD activity and computed tomography-measured visceral adipose tissue area (r=0.36, P < 0.05). Significant positive correlations were also found between omental 20-HSD activity and omental adipocyte diameter (r=0.49, P < 0.05) and omental adipose tissue LPL activity (r=0.36, P = 0.06). In conclusion, 20-HSD activity and mRNA were detected in SC and OM adipose tissue in women, and omental 20-hydroxylation of progesterone was highest in women with visceral obesity. Further studies are required to establish whether local conversion of progesterone may impact on the metabolism and function of adipocytes located within the abdominal cavity.