The study aimed to analyse the clinical courses of aggressively treated neonates with cytogenetically confirmed trisomy 18, with special attention focused on the efficiency of prenatal diagnostics, associated malformations, therapeutic dilemmas and outcomes. We investigated retrospectively the data concerning 20 neonates with trisomy 18, admitted to the Neonatal Intensive Care Unit (NICU) in Katowice between January 2000 and February 2005. Their birth weights ranged from 650 g to 2400 g, mean 1812 g; gestational age ranged from 27 to 42 weeks, median 38 weeks. Intrauterine growth retardation was noticed in 90% of neonates. Trisomy 18 was suspected prenatally in 40% of cases. Most (80%) of newborns were delivered by caesarean section (92% of neonates with prenatally unrecognized chromosomal defects, 62% of neonates with trisomy 18 suspicion) and 70% of infants needed respiratory support immediately after birth. Cardiac defects were present in 95%, central nervous system malformations in 65%, severe anomalies of digestive system or abdominal wall in 25% of patients. Nine surgical operations were performed during hospitalization (4 were palliative cardiac surgeries). Six patients (30%) survived the neonatal period and were discharged from the NICU. The median survival of the neonates who died was 20 days. In 4 cases cardiac problems implicated their death; in others, deaths were attributed to multiorgan failure, prematurity and/or infection. Further improvement of efficiency of prenatal ultrasound screening for diagnosis of trisomy 18 in the fetus is necessary. A lack of prenatal diagnosis of trisomy 18 in the fetus results in a high rate of unnecessary caesarean sections in these pregnancies. Despite the aggressive treatment most neonates with trisomy 18 died during the neonatal period. The majority of deaths were attributed to cardiorespiratory and multiorgan failure. Concerning the poor prognosis, prompt karyotyping (using FISH) of clinically suspected trisomy 18 is very important, because many invasive procedures and surgeries may then be avoided.