Background: Hypertrichosis following cast application is commonly observed after removing casts, due to an unknown mechanism. Objective: To determine the frequency and associated demographic and clinical risk factors of postcast hypertrichosis in patients who underwent cast application for bone fractures. Methods: The study included 117 patients (50 females, 67 males, age range: 3-91 years). Demographic information of each patient (age, gender, fracture localization, type of cast, cast duration and pruritus) was recorded. After removing the cast, the presence of hypertrichosis, contact dermatitis and lymphedema of the cast area was evaluated. Demographic and clinical features of the patients were analyzed to determine the risk factors for postcast hypertrichosis. Results: Postcast hypertrichosis was detected in 34.2% of patients. Patients with hypertrichosis were younger than those without hypertrichosis (p = 0.015). Duration of cast application, session of cast application, presence of lymphedema, contact dermatitis and pruritus between patients with hypertrichosis and without hypertrichosis were similar (p > 0.05). Age was the only parameter independently associated with developing postcast hypertrichosis (OR: 0.97, 95% CI: 0.95-0.99; p = 0.008). The frequency of hypertrichosis peaked significantly between 12 and 25 years (p = 0.026). Conclusion: A significant number of patients with cast application developed hypertrichosis. Patient age was closely associated with postcast hypertrichosis. Copyright (C) 2012 S. Karger AG, Basel