For the first time in Europe, the "Meconium Project" aimed to estimate the prevalence of drug use by pregnant women and the effects of exposure to illicit drugs during pregnancy on the fetus and infant. Between October 2002 and February 2004, 1151 (79%) dyads among the 1439 mother-infant dyads from the Hospital del Mar, Barcelona, Spain, met eligibility criteria and agreed to participate in the study. We present preliminary results on the first 830 meconium samples and 549 mother-infant dyads, for which statistical analysis of socio-economic and demographic characteristics and newborn somatometry was completed. The meconium analysis showed an overall 7.9% positivity for drugs of abuse, with 6-monoacetylmorphine and cocaine being the analytes, most frequently found in samples positive for opiates and cocaine. Structured interview disclosed 1.3, 1.8 and 1.3% of mothers exposed to opiates, cocaine and both drugs, while only one mother declared ecstasy consumption. Meconium analysis showed that prevalence of opiates, cocaine and combined drugs exposure was 8.7, 4.4 and 2.2%, respectively, and confirmed the case of ecstasy use. Arecoline, the main areca nut alkaloid, was found in meconium specimens from four Asiatic newborns, whose mothers declared beetle nut consumption during pregnancy. Parental ethnicity was not associated with drug use, nor was the social class, although a higher tendency toward drug consumption was observed in professional and partly skilled mothers. Drug consuming mothers showed a higher number of previous pregnancies and abortions (p<0.05) when compared to non-consumer mothers (meconium negative test), probably due to a lack of family planning. Consumption of opiates and cocaine during pregnancy was associated with active tobacco smoking, a higher number of smoked cigarettes and cannabis use. Exposure status and smoking behavior correlated with significantly lower birth weight in newborns from mothers exposed only to cocaine and to opiates and cocaine simultaneously. Of the four newborns exposed to arecoline, one showed a low birth weight, low intrauterine growth, hyporeflexia and hypotonia.