Objectives. To investigate the effect of sildenafil citrate treatment on serum dehydroepiandrosterone sulfate (DHEAS) levels in patients with erectile dysfunction (ED). Methods. A total of 124 men with a mean age of 45.9 years were included in the study. Group 1 consisted of 78 patients with ED, as determined by the Sexual Health Inventory of Male (SHIM) scale (score less than 2 1). Group 2 consisted of 46 healthy men with a SHIM score of 21 or greater. The 78 patients with ED took 100 mg sildenafil citrate at least eight times in 1 month. The SHIM scale was administered and serum DHEAS levels measured before and after treatment in the ED group. The serum DHEAS levels were also measured in the control group. The treatment response was defined as positive if the SHIM score was 21 or greater after sildenafil administration. Results. At the end of sildenafil citrate treatment, the serum DHEAS levels and SHIM scores had increased significantly in the ED group (P = 0.013 and P = 0.001, respectively). In groups 1 and 2, the mean pretreatment serum DHEAS level of the men younger than 50 years old was 200.1 +/- 77.9 and 279.4 +/- 125.4 mu g/dL, respectively (P = 0.013). The elevation of the serum DHEAS levels and SHIM scores was more significant in the sildenafil responders (P = 0.002 and P = 0.001), respectively. Conclusions. Serum DHEAS levels were significantly greater in the patients younger than 50 years old than in the older patients in the ED group. The serum DHEAS levels increased significantly after sildenafil citrate treatment in the ED group (especially in the younger men). Also, patient age was an important factor affecting the sildenafil citrate response.