Sulphasalazine is being used increasingly to treat rheumatoid arthritis, though its long term safety profile has not been established in this condition. The incidence and nature of adverse effects occurring in 774 patients with rheumatoid arthritis treated with sulphasalazine for periods ranging from one to 11 years were therefore noted. Altogether 205 of the patients stopped treatment permanently due to an adverse effect. One hundred and fifty six (76%) of these events occurred within three months and few beyond the first year. Most events were trivial and were self limiting after withdrawal of the drug; of the potentially more serious adverse effects, 33 (66%) occurred within three months of treatment. None of the patients died or suffered lasting ill effects. It is concluded that adverse effects of treatment with sulphasalazine are generally seen within three months; though regular monitoring is desirable during that period, thereafter few worrying problems occur.