Psoriasis is a chronic inflammatory skin disease. Associated comorbidities or risks may include psoriatic arthritis, obesity, depression, smoking, diabetes, hyperlipidemia, an increased risk of cardiovascular disease with myocardial infarction, or an increased risk of lymphoma. The clinical presentation of psoriasis can range from the more common red scaling elevated plaques on the elbows, knees, or scalp to the less common superficial pustules scattered on the palms or soles, or in rare cases wide-spread pustules on the body. More specifically, the clinical spectrum of psoriasis includes the plaque, guttate, small plaque, inverse, erythrodermic, and pustular variants. The determinants of the clinical severity of psoriasis, the risk of comorbidities, and the quality of life of a psoriatic patient are influenced by multiple factors. At the minimum, these include variations in the quality and type of psoriasis, the quantity of skin involved, and the distribution of skin lesions (including special areas such as the scalp, nails, face, intertriginous regions, and palmoplantar surfaces). Objective measures used to quantify the severity of psoriasis, including the body surface area involved, Physician's Global Assessment, Psoriasis Area and Severity Index, and quality of life measures, are all assessments that can be useful in guiding approaches to management and therapeutics. In this paper, we review the clinical spectrum of psoriasis, the differential diagnoses, measures and determinants of severity, and the recommendations on when to refer a patient to a specialist in psoriasis. We also briefly review the comorbidities, and note the importance of referring the psoriatic patient to the internist/general practitioner for evaluation and management for these comorbidities.