Phencyclidine, a frequently abused drug, has been shown to cross the placenta and may cause harmful effects in the fetus. Therefore, a prospective study was undertaken to determine the extent of phencyclidine use during pregnancy. Two thousand three hundred twenty-seven pregnant women were screened for phencyclidine use by questionnaire and enzyme-mediated immunoassay technique urine testing. Nineteen women were identified as using phencyclidine during pregnancy and 149 were past users. Women with a history of phencyclidine use were compared with a population sample of nonusers. Phencyclidine users were more likely to be white; they were also younger and of lesser parity than nonusers. The majority had a history of multiple drug abuse. Although 7.3% of the population gave a history of phencyclidine use and 0.8% were found to use the drug during pregnancy, these figures are believed to underestimate the problem.