A questionnaire was sent to potential participants of the III World Congress of in Vitro Fertilization and Embryo Transfer, held in Helsinki in 1984, concerning their current practice in and results with IVF to the end of January 1984. Sixty-five teams reported information concerning 10,028 cycles. Embryo replacement was performed in 7993 cycles to yield 600 infants to date from 523 confinements; 572 continuing pregnancies; 324 clinical abortions; and 19 ectopic and 285 "biochemical" pregnancies. The best success rates were seen in couples where the woman was less than 30 years of age (13.6%) compared with those where the woman was over 40 years of age (7.2%); where normal semen was used; where higher numbers of embryos were replaced per patient (9.7% with one, 14.6% with two, 19.3% with three, and 24.1% with four or more); and where the women presented with secondary infertility. Of the 523 confinements reported, 457 were singleton deliveries; 57 twin deliveries (10.9%); 7 triplet deliveries (1.3%); and two quadruplet deliveries (one set was born after January 1984). The cesarean section rate was 49%. No infant was reported to be born with a chromosomal abnormality. Nine conceptuses from spontaneous abortions were reported to have a chromosomal abnormality, but this is likely to be an underestimate since not all underwent chromosome analysis. There were 9 other severe fetal defects, including intrauterine fetal death (1.5%). Results of this collaborative study show that in vitro fertilization is widely accepted as a method for the treatment of infertility and does not carry a higher than normal risk of fetal abnormalities.