THE results of 7 pregnancies in 5 women suffering from phenylketonuria are reported. In 2 cases, low phenylalanine diet was introduced before conception and adhered to until after delivery. Both infants appeared to be normal at birth and have continued to develop satisfactorily, one now into the 3rd year of life and the other, now into the 4th year of life. Of the infants whose mothers started diet between 6 and 26 weeks gestation, all were microcephalic at birth, and of those old enough to have psychological assessments, none are in the normal range of intelligence. The mother of the 7th infant, in whom dietetic control was attempted after marriage, was completely unco-operative and defaulted. At 34-35 weeks gestation, she was admitted to the Maternity Hospital where she was restarted on low phenylalanine diet, and excellent control was achieved for the remaining weeks of pregnancy. She was delivered of a stillborn female infant with microcephaly, intrauterine malnutrition, but without cardiac abnormality.