Dercum's disease is a rare condition of painful subcutaneous growth of adipose tissue. Etiology is unknown and pain is difficult to control. We report the case of a 57-year-old man with generalized diffuse Dercum's disease, who improved after the treatment with transcutaneous frequency rhythmic electrical modulation system (FREMS). Treatment consisted in 4 cycles of 30 minutes FREMS sessions over a 6-month period. Measures of efficacy included pain assessment (visual analogue scale, VAS), adipose tissue thickness by magnetic resonance imaging, total body composition and regional fat mass by dual-energy X-ray absorptiometry, physical disability (Barthel index), and health status (Short Form-36 questionnaire). After FREMS treatment the patient's clinical conditions significantly improved, with reduction of pain on the VAS scale from 64 to 17 points, improvement of daily life abilities (the Barthel index increased from 12 to 18) and amelioration of health status (higher scores than baseline in all Short Form-36 domains). Furthermore, we documented a 12 mm reduction in subcutaneous adipose tissue thickness at the abdominal wall and a 7040 g decrease in total body fat mass. FREMS therapy proved to be effective and safe in the treatment of this rare and disabling condition.