Lafora body disease is one cause of progressive myoclonus epilepsy. It typically presents in the second decade with generalized seizures, myoclonus and then intellectual decline. Death is usual within 10 years. Diagnosis may be made by biopsy of skin, muscle, liver or brain. We present four siblings who were normal until their mid-twenties, but then developed intellectual decline, followed by myoclonus. Although a rare form of Lafora body disease has been described that follows a more benign course, may be of later onset, and whose pathology is subtly different, this family is so far unique in terms of the late presentation of otherwise typical Lafora body disease.