The safety of intracytoplasmic sperm injection (ICSI) as a novel procedure of assisted fertilization may be assessed by the health of the children born. In a prospective follow-up study of children born after assisted procreation, 130 children born consecutively after ICSI were compared with 130 control children born after in-vitro fertilization (IVF). In both groups, mothers were matched for age and had the same standard treatment protocol. There were 74 singleton, 50 twin and six triplet children in each group. Prenatal karyotyping and ultrasound screening, physical examination at birth and developmental milestones, with a follow-up at 2 months and 1 year, were recorded. Prenatal karyotypes were obtained in 100 of the 130 children in the ICSI group compared with 22 of the 130 children in the matched IVF group. All karyotypes were normal except for one prenatally detected mosaicism, which was not confirmed at birth. Four major malformations were detected in the ICSI group (holoprosecencephaly, femur fibula ulna syndrome and palatoschisis in two children), compared with six in the matched IVF group (coarctation of the aorta, palatoschisis, hypospadias, unilateral cryptorchidism, soft tissue syndactily and 11-beta-hydroxylase deficiency). In the ICSI and IVF groups, mean +/- SD birth weights were 2.94 +/- 0.67 and 2.80 +/- 0.73 kg, lengths were 48.46 +/- 3.56) and 47.47 +/- 5.78 cm, and head circumferences were 33.79 +/- 2.20 and 31.19 +/- 8.88 cm respectively. Among the ICSI singletons, the mean +/- SD birth weight was 3.28 +/- 0.58 kg and among the twins it was 2.60 +/- 0.43 kg; for the IVF singletons and matched twins the mean +/- SD birth weights were 3.19 +/- 0.56 and 2.36 +/- 0.61 kg respectively. In conclusion, there was no difference in the paediatric follow-up of 130 children born after ICSI and 130 children born after conventional IVF in age-matched control patients.