Williams syndrome (WS) is associated with a deletion of the elastin gene in over 90% of cases. We report maternal serum alpha feto-protein (MSAFP) levels in 5 women whose fetuses were later diagnosed as having WS. MSAFP levels ranged from 0.5-0.8 multiples of the median (MOM). Although further confirmation is necessary, it appears that MSAFP levels are lower than the median in WS. This apparent association has implications for counselling women following maternal serum screening.