鈥� We studied biopsy results in a kindred with the Lafora form of progressive myoclonic epilepsy. Four members of a family with known consanguinity presented as teenagers with seizures, myoclonus, dementia, and ataxia. After the diagnosis was established by brain biopsy in the first patient, many efforts were made to obtain a tissue diagnosis in the three other patients. Lafora bodies were absent in most of the skin biopsy specimens in three patients and in liver biopsy specimens from two patients. In cases of Lafora disease, where a reasonably certain clinical diagnosis can be established, supported by biopsy proof in some family members, repeated biopsy specimens even at advanced stages of the disease may be negative. These findings suggest that negative skin or liver biopsy specimens in patients with progressive myoclonic epilepsy should not exclude the diagnosis of Lafora disease.