The current study examined the singular and interactive effects of the 5-HTTLPR genotype and trait neuroticism on affective and physiological stress responses to an academic examination in healthy undergraduate students. From 771 students, 46 short/short (S/S)-allele carriers and 48 long/long (L/L)-allele carriers with the lowest and the highest neuroticism scores (80 females, 14 males; mean age+/-SD: 20.3+/-1.7 years) were selected. Salivary cortisol concentrations, mood and perceived stress were assessed before and after a 2-h written examination and compared with a control day. Negative mood, perceived stress and cortisol significantly increased during the examination compared to the control day. Negative stress effects on mood and perceived stress were significantly larger for S/S-allele carriers compared to L/L-allele carriers, regardless of trait neuroticism. Since vulnerability to real-life stressors is an important risk factor for depression pathogenesis, this may be a mediating factor making S/S-allele carriers more susceptible for depression symptoms.