Psoriatic arthritis (PsA), an inflammatory joint disease associated with psoriasis of the skin, has a heterogeneous pattern expressed by different manifestations, such as mild mono-oligoarthritis, a very severe, erosive and destructive polyarthritis indistinguishable from rheumatoid arthritis, and spondylarthropathy with axial involvement or enthesitis. The disease pattern often differs between patients as well as within the same patient over time. Measurable inflammatory activity is not always evident. Early detection of inflamed joints or axial involvement in patients with PsA is important in order to reduce the inflammation and prevent destruction, deformity and functional disability in the joints involved. Several factors, e.g., genetic, immunological, environmental and vascular, have been proposed to be of importance for the aetiology, the expression and prognosis of PsA. The basic treatment for PsA has been administration of non-steroid anti-inflammatory drugs (NSAIDs). Few disease modifying anti-rheumatic drugs (DMARDs) have been available due to a lack of efficacy of most of the DMARDs used for other rheumatic diseases. New insights into genetic, immunological and vascular factors in PsA are of interest as possible targets for future therapy and will be discussed in this review.