A total of 258 women requiring assisted delivery where vacuum extraction was thought to be suitable were randomly allocated to delivery with a new silicone rubber cup or metal vacuum extractor cups. There was a tendency for the silicone rubber cup to effect delivery more quickly and to cause less scalp trauma, but to fail to effect delivery on more occasions than metal cups. However, none of these differences was statistically significant. There were no statistically significant differences in the rates of birth canal trauma, maternal blood loss, or neonatal jaundice. The silicone rubber cup produced a cosmetically more acceptable chignon than the metal cups. The introduction of vacuum extractors with silicone rubber cups into obstetric units should be encouraged.