Thirteen cases of trisomy 18 (T18) were ascertained clinically and cytogenetically during the period 1984-1986. Eight cases were delivered during 1986 in the Maternity Hospital out of 17,318 live births, making an incidence of 4.61/10,000, which is significantly higher than the international incidence as well as the incidence in previous years. The female-to-male sex ratio was 1.8/1, the median maternal age 32.5, and the median paternal age 40. There was no history of polyhydramnios. Five cases were delivered by cesarean section and four cases died in the neonatal period. All cases proved to be full trisomy 18 with no mosaicism detected; in one case parental inversion 9 was detected.