There is no standard definition regarding the severity of psoriasis, and a number of factors should be considered, including the extent and stability of skin disease, involvement of joints, response to treatment, and impact on quality of life. Erythrodermic psoriasis and pustular psoriasis are severe conditions and the patient may be systemically unwell and febrile. NICE recommends that four key areas should be evaluated and recorded when assessing patients: severity, using the static Physician's Global Assessment (sPGA); disease impact on physical, psychological and social wellbeing using the Dermatology Life Quality Index (DLQI); the presence of psoriatic arthritis; and comorbidities. Ideally, patients should be assessed annually for psoriatic arthritis: the Psoriasis Epidemiology Screening Tool is a validated tool to screen for psoriatic arthritis in primary and secondary care. Patients with severe psoriasis should undergo cardiovascular risk assessment at presentation and every five years, or more frequently if indicated. Referral to secondary care should be made for patients with any type of psoriasis with poor response to topical therapy (after 2 or 3 months according to SIGN) and for extensive psoriasis. Cases where the psoriasis is having a significant physical or psychological impact on an individual's quality of life warrant early referral, as do those where the diagnosis is uncertain. Patients with generalised pustular psoriasis or erythroderma should be referred urgently for same-day specialist input. Patients with acute guttate psoriasis who may require phototherapy should also be referred. Children and adolescents with any type of psoriasis should be referred to a specialist at initial presentation.