The inconsistent findings on the association between COMT (catecholamine-O-methyl-transferase) and suicidal behaviour gave reason to choose a clear phenotype description of suicidal behaviour and take childhood maltreatment as environmental factor into account. The aim of this candidate-gene-association study was to eliminate heterogeneity within the sample by only recruiting affective disorder patients and find associations between COMT polymorphisms and defined suicidal phenotypes. In a sample of 258 affective disorder patients a detailed clinical assessment (e.g. CTQ, SCAN, HAMD, SBQ-R, VI-SURIAS, LPC) was performed. DNA of peripheral blood samples was genotyped using TaqMan® SNP Genotyping Assays. We observed that the haplotype GAT of rs737865, rs6269, rs4633 is significantly associated with suicide attempt (p = 0.003 [pcorr = 0.021]), and that there is a tendency towards self-harming behaviour (p = 0.02 [pcorr = 0.08]) and also NSSI (p = 0.03 [pcorr = 0.08]), though the p values did not resist multiple testing correction. The same effect we observed with the 4-marker slide window haplotype, GATA of rs737865, rs6269, rs4633, rs4680 (p = 0.009 [pcorr = 0.045]). The findings support an association between the COMT gene and suicidal behaviour phenotypes with and without childhood maltreatment as environmental factor.