Ehlers-Danlos syndrome type IV (EDS-IV) is an autosomal-dominant disorder caused by a defect of type III collagen which leads to ruptures of arteries and hollow organs. Neurological presentation with muscle involvement and flexion contractures of the finger joints is uncommon. We clinically characterized seven members of a family with EDS-IV. The index patient, a young woman with an acrogeric face, suffered chronic muscle pain and cramps, Achilles tendon retraction, finger flexion contractures and seizures. The mother had similar features and had experienced an ischemic stroke. Biochemical study in cultured fibroblasts and molecular analysis of the COL3A1 gene led to the diagnosis of EDS-IV. A glycine substitution, p.G883V, within the triple helix of the alpha 1(III) chain, was found in the index patient and in the mother. The maternal grandfather and an aunt each had an abdominal aortic aneurysm, the rupture of which was the cause of death in the latter, at 40 years of age. Surprisingly, we found the mutation, as a mosaic, in the asymptomatic maternal grandmother. This expands the clinical spectrum of EDS type IV and confirms that in some families mosaicism can be identified as the source of the mutation.