This study was based on 156 cases of fibromatoses seen at the Soft Tissue Branch of the Armed Forces Institute of Pathology, the Australian Soft Tissue Tumour Registry and the Institute of Medical and Veterinary Science, Adelaide. There were 86 'adult' fibromatoses, 50 'juvenile' fibromatoses, and 20 unclassified lesions. 'Adult' fibromatoses, found predominantly in patients older than 20 yr, fell into 2 main groups; the Dupuytren type fibromatoses (27) and the desmoid tumours (59). In the former group, there were 5 cases of palmar fibromatosis, 15 of plantar fibromatosis, 3 knuckle pads (dorsal fibromatosis), 4 lesions resembling palmar fibromatosis in unusual locations, and no cases of Peyronie's disease. In the desmoid group, there were 13 abdominal desmoids, 39 extra-abdominal desmoids, one mesenteric fibromatosis, 3 examples of multiple extra-abdominal desmoids, one of abdominal desmoid and mesenteric fibromatosis, and 2 of Gardner's syndrome. Six desmoids occurred in scars. There were no cases of multiple familial desmoids. 'Juvenile' fibromatoses occurred predominantly or exclusively in the first 2 decades of life. There were 11 congenital 'fibrosarcomas', 2 congenital generalized fibrornatoses, 8 solitary lesions resembling congenital generalized fibromatoses, 4 fibromatosis colli, 3 diffuse infantile fibromatoses, 5 fibrous hamartomas of infancy, 5 recurring digital tumours of childhood and 12 juvenile aponeurotic fibromas. As a group, the fibromatoses are best regarded as non-metastasizing proliferations of fibrous tissue which may recur locally after excision. They may be both multiple and familial, their growth rate frequently decreases after an initial period of rapid growth, and they may regress spontaneously. This study was based on 156 cases of fibromatoses seen at the Soft Tissue Branch of the Armed Forces Institute of Pathology, the Australian Soft Tissue Tumour Registry and the Institute of Medical and Veterinary Science, Adelaide. There were 86 'adult' fibromatoses, 50 'juvenile' fibromatoses, and 20 unclassified lesions. 'Adult' fibromatoses, found predominantly in patients older than 20 yr, fell into 2 main groups; the Dupuytren type fibromatoses (27) and the desmoid tumours (59). In the former group, there were 5 cases of palmar fibromatosis, 15 of plantar fibromatosis, 3 knuckle pads (dorsal fibromatosis), 4 lesions resembling palmar fibromatosis in unusual locations, and no cases of Peyronie's disease. In the desmoid group, there were 13 abdominal desmoids, 39 extra-abdominal desmoids, one mesenteric fibromatosis, 3 examples of multiple extra-abdominal desmoids, one of abdominal desmoid and mesenteric fibromatosis, and 2 of Gardner's syndrome. Six desmoids occurred in scars. There were no cases of multiple familial desmoids. 'Juvenile' fibromatoses occurred predominantly or exclusively in the first 2 decades of life. There were 11 congenital 'fibrosarcomas', 2 congenital generalized fibrornatoses, 8 solitary lesions resembling congenital generalized fibromatoses, 4 fibromatosis colli, 3 diffuse infantile fibromatoses, 5 fibrous hamartomas of infancy, 5 recurring digital tumours of childhood and 12 juvenile aponeurotic fibromas. As a group, the fibromatoses are best regarded as non-metastasizing proliferations of fibrous tissue which may recur locally after excision. They may be both multiple and familial, their growth rate frequently decreases after an initial period of rapid growth, and they may regress spontaneously.