The objective was to report a clinical, pathological and muscle magnetic resonance (MR) study of an Italian family with an autosomal dominant inclusion body myopathy (AD-IBM). Eight subjects (age range 20-56 years; 5 females and 3 males) belonging to four generations were studied. Onset of disturbances (distal weakness at lower limbs) ranged from 20 to 28 years. CK levels were increased to five times. Only in an early stage oedema of involved muscles has been demonstrated by muscle MR. Quadriceps femoris was characteristically spared; in the last phases a mild involvement of the vasti became evident with persistent sparing of the rectus femori. Rimmed vacuoles and hyperphosphorylated tau filaments were evident at muscle biopsy. Linkage analysis excluded the association of the disease to chromosome loci 14q11, 17p13.1, 2p13, 19p13. The study suggests that quadriceps sparing is a characteristic feature also of AD-IBM. This finding could represent a muscle-image hallmark helpful in diagnosis of autosomal dominant muscular disorders.