Joint diseases are common among patients with psoriasis. Psoriatic arthritis, the most important of these, can be defined as a rheumatoid factor-negative inflammatory arthritis associated with psoriasis and has emerged as a specific disease independent from rheumatoid arthritis. Psoriatic arthritis is divided into several clinical subsets, which is helpful in differentiating it from other types of inflammatory arthritis. The prevalence of arthritis in patients with psoriasis may be far higher than the previously accepted average of 7%. In a recent study of 5,795 members of the Nordic Psoriasis Associations, the prevalence was found to be 30%. Arthritis has a significant impact on quality of life in patients with psoriasis. These factors should be recognised as they have implications for therapy, since a number of drugs can delay or stop joint damage when given in time. This also applies to the new biologic agents, although at present these therapies are generally restricted to patients non-responsive to other available drugs. Alone or in combination, the new drugs may achieve higher response rates and have better safety profiles than older therapies. However, long-term experience is still lacking and, unfortunately, the new drugs will be far from affordable by all for some time to come.