Hereditary motor and sensory neuropathy (HMSN) is one of the most frequently inherited causes of peripheral neurological disability. To date, the classification has been based on clinical, histological and genetic grounds. Due to increased genetic knowledge at the molecular level in recent years, diagnosis of the different subtypes has been considerably improved and their relationship clarified. We describe three generations of a family with HMSN IA (Charcot-Marie-Tooth disease IA = CMT 1A) with a genetic defect mapped to chromosome 17 and show the importance of genetic testing. Even in benign and clinically non-manifested causes of the disease, an early and non-invasive diagnosis should be made by genetic testing to identify affected persons; thus, nerve biopsy can be abandoned. Operations of pes cavus, which are not indicated and are often complicated by delayed healing, may be avoided. Instead, patients should undergo early physiotherapy and be counselled about their professional careers and family planning.