Pyoderma gangrenosum (PG) is an idiopathic, inflammatory, ulcerative disease of undetermined cause. The diagnosis is based on clinical and pathologic features and requires exclusion of conditions that produce ulcerations. An atypical bullous variant (atypical pyoderma gangrenosum, APG) exists with clinical features similar to those of Sweet syndrome. Because PG is a rare disease, few large case series have been reported. Pyoderma gangrenosum was first recognized as a unique disease entity in the first half of the 20th century. Cumulative knowledge of PG is based on a handful of case series and multiple individual case reports. To augment that knowledge, we present our experience with a large number of patients over a significant time. We performed a retrospective analysis of the medical records of 86 patients with PG who were evaluated and treated over 12 years at 2 university-based dermatology departments. The mean (+/- standard deviation) age of onset of PG and APG, respectively, was 44.6 +/- 19.7 years and 52.2 +/- 15.3 years. Lower extremity involvement was most common in PG, whereas upper extremity involvement was most common in APG. Associated relevant systemic diseases were seen in 50% of patients. Inflammatory bowel disease was the most common association in patients with PG, whereas hematologic disease or malignancy was most common in those with APG. Although a few patients were managed with local measures or nonimmunosuppressive treatment, the majority required oral corticosteroid therapy, often with systemic immunosuppressive treatment. PG patients required a mean 11.5 +/- 11.1 months of treatment to achieve remission compared with 9.0 +/- 13.7 months for patients with APG. Five patients (5.8%) had disease that was extremely refractory to multiple intensive therapies. The prognosis and disease associations for PG and APG appear to be different. Compared with PG, APG is more often associated with hematologic disease or malignancy, and remits more quickly.