A thirty-year-old dental surgeon who worked until the 35th week of pregnancy in a surgery in which mercury vapour concentrations in excess of the threshold limit value (TLV) had been detected, gave birth at 42 weeks to a small-for-dates baby with severe brain damage. The possibility that this baby's development might have been harmed by mercury is discussed and the literature relevant to teratogenicity of mercury reviewed. Attention is drawn to the need for further research into the effects on health and pregnancy outcome of mercury vapour in dental surgeries.