To investigate the clinical effect of vitamin D supplementation on psoriasis from a community-dwelling population.Participants with psoriasis in a large randomized controlled trial examining the effect of vitamin D supplementation (100,000 IU monthly) in adults aged 50-84 years were invited to participate in a psoriasis sub-study over 12 months. The primary outcome was the Psoriasis Area and Severity Index (PASI) and secondary outcomes were Physicians Global Assessment (PGA), Dermatology Life Quality Index (DLQI), and Psoriasis Disability Index (PDI). Trial identification number ACTRN12611000402943.Twenty-three were allocated to vitamin D and 42 to placebo. There was no significant difference at baseline between the two groups. Mean (SD) baseline 25-hydroxyvitamin D was 65.7 (25.7) nmol/L. There were no significant differences (p > .05) between the groups in all of the psoriasis outcome measures. Mean scores [95% CI] at 12 months for the Placebo versus Vitamin D groups: PASI 2.2 [1.4, 3.0] versus 2.1 [1.0, 3.2]; PGA 1.4 [1.1, 1.7] versus 1.5 [1.1, 1.9]; PDI 2.1 [0.9, 3.2] versus 1.9 [0.4, 3.4]; and DLQI 2.5 [1.4, 3.6] versus 2.0 [0.5, 3.4].Vitamin D supplementation (100,000 IU per month) is not recommended as a treatment for mild psoriasis.