We describe 8 patients with muscle carnitine deficiency, 7 males and 1 female, varying in age from 5 days to 64 years. Seven had decreased muscle strength and all had increased lipids droplets in the muscle biopsy. The symptoms began in the first days of life in three cases, in childhood in two, in adult life in two, while one case was free of symptoms at age 64 (heterozygote?). Some patients had difficulty chewing, dysphagia, hypotonia and splenomegaly; one patient had a fluctuating clinical course. All had elevated serum enzymes, mainly creatine-kinase. The electromyogram showed primary muscle involvement in one case, denervation in two, "mixed" features in two and was not done in three. The muscle biopsy, beside lipid storage, showed denervation in four, chronic myopathy in four and type II fiber atrophy in one. In two cases, histological findings suggested infantile spinal muscle atrophy. One patient appeared to have a systemic form of carnitine deficiency, with severe myocardial involvement and died of heart failure before treatment was initiated. A discussion about clinical findings, metabolism and therapeutic aspects of muscle carnitine deficiency is made.