Abstract: The overlap syndrome is a vague entity in the group of connective tissue diseases. It is unclear whether it is fortuitous association of two or more connective tissue diseases (CTD), or a distinct disease. The early description of this syndrome was "a collection symptoms of CTD and the existence of anti - nRNP antibody". Many studies however, show that the anti - nRNP antibody is not specific for diagnosis. The aim of this study was to demonstrate the clinical and laboratory features of the overlap syndrome in 70 patients with SLE and 49 patients with PM/DM. The main features were then compared with those of the non overlapped disease (SLE or PM/DM) to search for any differences. Sharp, who first described this syndrome believed that the disease was a benign one. We compared the type of the treatment and the mortality rate. Our results seem to show that the overlap syndrome is not a fortuitous association of two or more diseases. There are differences separating an overlap syndrome from any of the original CTD. In contrast to the original belief of Sharp, the overlap syndrome is not a benign entity.