In the present study, we investigated the effects of paternal smoking on the frequency of Chromosomal Aberrations (CAs) in newborns. Newborns and their mothers who participated in this study were from Ankara Hospital, Gynecology and Obstetrics Clinics, comprised of 31 newborns of smoking fathers and 31 newborns of non-smoking fathers. In order to quantify the degree of maternal exposure, we detected the levels of urinary cotinine in the mothers. (CAs) were analyzed in umbilical cord blood samples and the levels of urinary cotinine were detected in The mothers' urine samples by gas chromatography. We found a significant increase in the frequency of CAs in the newborns exposed to paternal smoking when compared to paternal non-smokers (1.45±1.52 and 1.19±1.30, respectively, p=0.05). Our results indicated that paternal smoking increases the frequency of CAs and may make a substantial contribution to newborn exposure. We also found that urinary cotinine: creatinine ratios were the highest in women whose husbands smoked more than 20 cigarettes per day.