<b><i>Background:</i></b> We hypothesized that DNA variants affecting neurodevelopment such as rs4307059 <i>(CDH10/CDH9)</i>, rs930752 <i>(NRXN1)</i>, rs6265 <i>(BDNF)</i> or rs10868235 <i>(NTRK2)</i> may predispose to completed suicide. <b><i>Methodology:</i></b> We used a case-control two-stage approach based on a discovery cohort (557 cases and ∼550 controls) and replication cohort (159 cases and 186 controls). The suicides were ascertained as consecutive cases autopsied at the Department of Forensic Medicine, Medical University of Warsaw, Poland. <b><i>Results:</i></b> In the discovery cohort we found an association between suicide and the CC genotype in the rs4307059 polymorphism (OR 1.64, p = 0.012). The trend for an overrepresentation of the CC homozygotes among suicides was replicated in the second cohort (OR 1.97, p = 0.056). Analysis in the pooled cohorts showed that rs4307059 CC was associated with completed suicide (OR 1.71, p = 0.002) also after Bonferroni correction (p_cor. = 0.024). In an exploratory search for genotype-phenotype correlation we found that males with the rs4307059 CC genotype committed suicide earlier than those with CT/TT genotypes (p = 0.049). <b><i>Conclusions:</i></b> The CC genotype of rs4307059 located in the region between <i>CDH9</i> and <i>CDH10</i> is associated with completed suicide in a Polish cohort.