Background Psoriasis exerts a profound negative impact on health-related quality of life (QoL). Although the severity of psoriasis is one potential variable that contributes to decreased QoL, previous studies have shown only weak or no association between measures of psoriasis severity and QoL. We hypothesized that this relationship is moderated by temperament factors. Objective We aimed to verify whether the relationship between disease severity and QoL is moderated by a constellation of temperament traits (i.e., temperament risk factors) and whether this moderation takes place via cognitive-appraisal and coping processes. Methods One hundred fifty patients with psoriasis vulgaris participated in the study. Psoriasis severity was assessed by a standardized measure, the Psoriasis Area and Severity Index (PASI), and the patients also completed a battery of psychological questionnaires assessing QoL, temperament, disease-related cognitive appraisals, and coping strategies. Results A specific constellation of temperament traits was found to moderate the strength of the association between the PASI and QoL. This constellation of temperament traits was associated with certain disease-related cognitive appraisals (i.e., threat, obstacle/loss, harm, profit, value) and emotion-focused coping strategies (i.e., self-blame, avoidance, resignation, seeking social support, and seeking information). Conclusion The constellation of temperament traits is a crucial individual variable that strongly moderates the negative impact of psoriasis severity on QoL, potentially through the activation of non-adaptive cognitive appraisals and coping strategies in susceptible individuals.