Abstract BACKGROUND: Chronic plaque psoriasis is frequently associated to metabolic disorders including obesity. Anti-TNF-alpha treatments can induce body weight increase in patients with psoriasis. Information on the effect of ustekinumab on the body weight is not available. OBJECTIVE: To investigate whether therapy with ustekinumab is associated with changes in body mass index (BMI) in patients with chronic plaque psoriasis. METHODS: A prospective, multi-center study comparing the changes in BMI in two closed cohorts of psoriatic patients during 7-month treatment with ustekinumab (N=79) or infliximab (N=83). RESULTS: Patients treated for 7 months with infliximab showed a significant (p< 0.001) increase in BMI (2.1% ± 4.5, mean ± SD) and body weight (+2.5 ± 3.3 kg) compared to patients treated with ustekinumab (0.1% ± 3.3; 0.6 Kg ± 1.1). 45% of patients treated with infliximab had a BMI increase greater 2% compared to only 11% of those receiving ustekinumab (p=0.01). At the multivariate analysis, any other clinical parameters predicted the BMI increase except for the use of infliximab. At month 7, 96% of patients treated with infliximab and 82% of patients treated with ustekinumab achieved at least a 50% improvement from their baseline PASI (PASI 50) and 69% of the infliximab group compared to 58% of ustekinumab group achieved at least a 75% improvement (PASI 75). There was no difference in the proportion of PASI 50 and PASI 75 responders between the two groups. CONCLUSIONS: In contrast to infliximab, ustekinumab does not increase BMI in patients with chronic plaque psoriasis. This difference could be taken into account in the selection of biologics for treating patients with psoriasis.