Background: Pyoderma gangrenosum (PG) is a rare, painful ulcerating skin condition that is often associated with underlying systemic disease such as inflammatory bowel disease, rheumatoid arthritis and haematological malignancies. There has been little research done into treatments for the disease. Aims: The STOP GAP trial will be the first trial to investigate the two most commonly used treatments for PG. The study aims to test the hypothesis that ciclosporin (Neoral®) is more effective than systemic prednisolone for the treatment of PG. One hundred and forty patients will be recruited by April 2012. Methods: Patients with a clinical diagnosis of PG are being recruited from around 50 dermatology departments in secondary care trusts in the UK. They are being randomised to either prednisolone (0.75 mg/kg/day) or ciclosporin (4 mg/kg/day). For cases where topical therapy is indicated, patients are being entered into a parallel observational study. Results: The study is ongoing and results should be published by August 2013. Conclusions: The STOP GAP trial is now the largest randomised controlled trial (RCT) ever conducted in PG and will provide clinicians with an evidence base for the treatment of this debilitating condition for the first time.