Psoriatic arthritis (PsA) is a common form of inflammatory arthritis but is underdiagnosed. Psoriasis affects over 1.5% of the UK population. Around 15% of these patients will be diagnosed with PsA, but up to 40% may have evidence of arthritis if reviewed thoroughly. PsA can be difficult to diagnose as patients present with a variety of different patterns of arthritis. Most patients with PsA have relatively mild skin psoriasis, but some have more significant disease. Only 10-20% develop arthritis before their skin disease. Many patients have mild skin psoriasis that they are unaware of, or have not had diagnosed. Joint involvement is far more variable in PsA, compared with rheumatoid arthritis, and patients may present with: monoarthritis; oligoarthritis; involvement of the distal interphalangeal joints; a rheumatoid arthritis-like picture with multiple joints involved including the small joints in the hand or axial disease producing symptoms similar to ankylosing spondylitis. Features such as dactylitis (uniform sausage-like swelling of the whole digit either finger or toe) and enthesitis (inflammation at the sites of muscle or tendon attachment to bone) may also help diagnose PsA. Skin disease is present in the majority of patients although not all. Hidden areas for psoriasis include: behind the ears; at the top of the natal cleft and around the umbilicus. Larger joints, particularly the knees, can develop very big effusions causing obvious swelling. Areas to test for enthesitis should include the Achilles tendon, plantar fascia, costochondral joints and the elbow. Patients with suspected PsA should be referred promptly to a rheumatologist for further assessment and treatment. Diagnosis of PsA can be made on clinical grounds but blood tests and radiographs are performed routinely to aid diagnosis. Initial therapy for PsA should include NSAIDs to ease pain and stiffness. Local injections of corticosteroids are recommended for peripheral arthritis (given IA) and dactylitis (usually by injection into the flexor tendon or adjacent joints). DMARDs are routinely used to treat all aspects of psoriatic disease, except spinal disease, and prescribing should be initiated by a specialist.