Desmoid-type fibromatosis (DF) is a rare mesenchymal tumor occurring in only 2 to 4 people per 1,000,000 population a year. Desmoid tumors are either seen sporadically or in individuals with familial adenomatous polyposis (FAP). The etiology of sporadic DF is uncertain. The aim of this study was to estimate the potential significance of germline mutations in the АРС gene in patients with sporadic DF. АРС exons were amplified, studied using conformation sensitive gel electrophoresis and then Sanger-sequenced. The obtained data were processed in Statistica 10. Mutations were detected in 6 (12%) of 51 participants with sporadic DF. Those 6 patients shared a typical DF phenotype characterized by early age of onset (5.8 years on average, in contrast to the patients without APC mutations, who developed DF at 19 years of age; р = 0.02), severe clinical course, multifocal localization on the trunk, and poor prognosis. All of the detected APC mutations were localized to the 3'-end of the gene. For the purpose of comparison, we analyzed a sample of 12 patients with FAP-associated DF. Of those patients, 6 carried mutations in the APC gene. In the analyzed sample, the patients with FAP and the mutant APC gene developed DF at older age (35 years) than the patients with sporadic DF (p = 0.004) and their tumors were not multifocal. This means that sporadic and FAP-associated desmoids have different phenotypes in patients with APC mutations. Patients with sporadic tumors have mutations at the 3'-end of the АРС gene more often than individuals with FAP-associated DF. To our knowledge, this is the first study to characterize the subtype of sporadic desmoid fibromatosis phenotypically determined by germline mutations in the APC gene.