The authors studied the familial occurrence of fibromyalgia (FMS) to determine a possible role of genetic and familial factors in this syndrome. Fifty-eight offspring aged 5 to 46 years (35 males and 23 females) from 20 complete nuclear families ascertained through affected mothers with FMS were clinically evaluated for FMS according to the ACR 1990 diagnostic criteria. FMS symptoms, quality of life, physical functioning, and dolorimetry thresholds were assessed in all subjects. Sixteen offspring (28%) were found to have FMS. The M/F ratio among the affected was 0.8 compared with 1.5 in the whole study group. Offspring with and without FMS did not differ on anxiety, depression, global well-being, quality of life, and physical functioning. A high prevalence of FMS was observed among offspring of FMS mothers. Because psychological end familial factors were not different in children with and without FMS, the high familial occurrence of this syndrome may be attributable to genetic factors.