Study of phenotype and familial distribution of malignant hyperthermia (MH) suggests heterogeneity with MH possibly being a symptom of several disorders. Review of all reported family studies supports the concept of heterogeneity with autosomal dominant inheritance in about one-half of the families. There is no strong evidence for other mendelian patterns of inheritance, but sporadic and possibly multifactorially determined cases are common. MH is also seen in other musculoskeletal disorders. We report 12 Wisconsin families with MH and outline a preliminary approach to the counseling of MH patients and their families.