Congenital pseudarthrosis of the tibia is a rare disease with a variable history. The pseudarthrosis is usually not present at birth (and therefore is not truly congenital) but occurs during the first decade of life. Paget in 1891 was the first to describe a case. The etiology is unknown. Neurofibromatosis plays a role in approximately 50% of patients. In the others, hereditary and mechanical factors are debated. Various (morphologic) classification systems have been proposed (Andersen, Boyd, Crawford). Because the appearance changes during the course of the disease, all classification systems have limited value: the determining factor is the stage of the disease at which it was classified. Because of the rarity of the disease and the variability of its history, the European Pediatric Orthopaedic Society decided to carry out a multicenter study on this disease. This paper presents the epidemiologic data on the patients involved. Data have been gathered on 340 patients from 13 countries. Two hundred patients were male (58.8%), 140 were female (41.2%). The right side was affected in 165 patients (48.5%) and the left side in 172 (50.6%); 3 patients had bilateral disease. Symptoms of neurofibromatosis were present in 54.7%. Histologic examinations in 192 patients showed a nonspecific appearance in 45.3%; in 15.6% the ultrastructure resembled fibrous dysplasia, and in 39% there was histologic evidence of neurofibromatosis. Most of the lesions were initially localized in the middle or distal third of the tibia. In 29% the localization changed during the course of the disease.