Introduction Psoriasis is a chronic inflammatory and immunemediatedskin disease that affects over 7.2 million U.S. adults. Currenttreatment has improved clinical outcomes. Vitamin D is believed toaffect the proliferation and regeneration of keratinocytes; therefore,its deficiency is a possible risk factor; however, there is still no definiteevidence. The objective of this study was to synthesize existing dataon the relationship between hypovitaminosis D and psoriasis. Methods. A meta-analysis of relevant studies was conducted bydoing a comprehensive search in the MEDLINE, EMBASE, and theCochrane Central Register through July 2018 to identify relevantcohort studies and to assess serum 25-hydroxyvitamin D (25(OH)D) levels in adults with psoriasis. The primary outcome was the meandifference in serum 25(OH)D level between psoriatic patients andcontrols. Results The initial search identified 107 articles. Only ten studiesmet the criteria for full-paper review. Meta-analysis was conductedfrom ten prospective cohort studies involving 6,217 controls and 693cases. The pooled mean difference in serum 25(OH)D level betweenpsoriatic patients and controls was -6.13 ng/ml (95% CI, -10.93 to-1.32, p-value = 0.01). The between-study heterogeneity (I2) was98%, p < 0.00001. Conclusion Our meta-analysis was the first study to establish therelation between vitamin D and psoriasis. The result found a significantrelationship between low 25(OH) D levels and psoriasis, but didnot establish a causal relationship. Further studies will be requiredto establish whether vitamin D supplementation benefits patientswith psoriasis.