All participants (N=157) who completed the set of moral dilemmas (cf. Conway & Gawronski, 2013) were successfully genotyped for 5-HTTLPR. Genotype distribution was as follows: LL = 69 (43.9%), LS = 72 (45.9%), and SS = 16 (10.2%). Genotype distribution did not deviate from HWE (p = .659). LS and SS genotypes were grouped together and contrasted with LL homozygotes. There was no main effect of 5-HTTLPR on the traditional moral judgement score, deontology or utilitarianism. However, there was a significant interaction between 5-HTTLPR and endocrine status (men vs. free cycling women vs. women using combined oral contraceptives; COC) on deontology. In men and free cycling women, LL genotypes showed significantly reduced levels of deontology compared to S allele carriers. Contrariwise, in women using COC LL genotypes had higher levels of deontology compared to S allele carriers, although the effect did not reach significance. There was no interaction effect on the traditional score or on utilitarianism. There were no effects of 5-HTTLPR or 5-HTTLPR x endocrine status on response times. However, while overall difficulty ratings were also unaffected by 5-HTTLPR, there was a genotype x response type (pro vs. contra harmful actions) interaction. LL homozygotes rated decisions for harmful actions as less difficult than decisions against harmful options while the opposite was true for S allele carriers. Previous findings on 5-HTTLPR and moral judgements are mixed. LL homozygotes have been reported to show increased endorsement of harmful actions for the greater good (Marsh et al., 2011; Martinez, 2020). However, a recent study in a large sample found that SS homozygotes rated (impersonal) harm as more permissible (Yang et al., 2019). Our own findings point to exogenous gonadal steroids as potential modulators.