OBJECTIVES: Psoriasis patients often experience delay in diagnosis. This study examined the diagnoses of skin diseases and treatments before receiving psoriasis diagnosis among patients with moderate-to-severe psoriasis. METHODS:  Adult patients with at least 2 psoriasis diagnoses (ICD-9-CM code: 696.1) between 01/1998 and 03/2015 were identified in the OptumHealth Reporting and Insights claims database. The index date was the first psoriasis diagnosis date. Eligible patients had continuous eligibility during the 3 years before (baseline period) and 5 years after the index date. Patients with moderate-to-severe psoriasis were identified if they had ≥1 systemic therapy or phototherapy during the 5-year post-index period. Diagnoses of other skin diseases, time from the first skin disease diagnosis to the first psoriasis diagnosis and treatments for skin diseases were described over the baseline period RESULTS: The study included 1,098 patients with a mean age of 53 years and 46% female. Common psoriasis-related comorbidities during the baseline period were hyperlipidemia (41%), hypertension (38%), and diabetes (14%). During the baseline period, 474 (43%) patients had ≥1 diagnosis of other skin disease, with the most common including contact dermatitis and other eczema (29%), dermatophytosis (13%), and atopic dermatitis and related conditions (7%). The average time from the 1^st skin disease diagnosis to the 1^st psoriasis diagnosis was 15.9 months. Among patients with a skin disease diagnosis, 91% received treatments related to skin diseases with the most commonly used being steroids (topical: 77%, non-topical: 24%) and antifungals (topical: 39%, oral: 23%). CONCLUSIONS: A high proportion of moderate-to-severe psoriasis patients had diagnoses for other skin diseases and was treated with steroids or antifungals before receiving the 1^st psoriasis diagnosis. The high rates of other skin disease diagnoses at baseline suggested that some patients may be misdiagnosed. Future studies assessing the association between these skin diseases and psoriasis are warranted.