Bowen's disease is an in situ squamous cell carcinoma of the skin with various treatment modalities available. A major advantage of surgical excision is the opportunity to histologically examine the resection margins. There is no consensus about the most appropriate margin. This retrospective study evaluates the clearance rates achieved by excision with a 5 mm margin and estimates how that might change after fictitiously reducing the resection margin by 1 or 2 mm. Patients with histologically confirmed Bowen's disease were selected at the Maastricht University Medical Centre from 2002 until 2007. Surgical margins and complete excision rates were evaluated and histological slides were re-examined. To our knowledge this is the first study investigating the safety margin for Bowen's disease. As Bowen's disease is not an invasive disease, minimisation of healthy tissue excision is desirable. Our data show that a hypothetical reduction of the safety margin from 5 mm to 4 or 3 mm decreases the complete excision rate from 94.4% to 87% and 74.1%, respectively.