There are few studies evaluating the cost-effectiveness of self-management interventions for patients with psoriasis. Motivational interviewing (MI) as a telephone follow-up after climate-heliotherapy was effective on several clinical parameters, but its cost-effectiveness is unknown. A cost-utility analysis was conducted alongside a randomized controlled trial (RCT) comparing MI with usual care. A total of 169 Norwegian patients were included. A within-trial analysis compared the costs and quality-adjusted life years (QALYs). Utilities were measured with the 15D instrument, supplemented with Dermatological Life Quality Index (DLQI). A time-integrated summary score defined the clinical effects. QALYs were adjusted for baseline differences. MI provided equivalent quality of life and utility (15D: -0.0022 QALYs (95% Cl -0.02, 0.01), p = 0.77, and DLQI: -0.62 QALYs (95%CI -0.65, 0.41), p = 0.24, at lower costs €-1103 (-2293, 87), p = 0.058, compared with treatment-as-usual. The MI intervention was thus cost-effective. This result was more evident when using the DLQI as outcome measure compared with 15D.