Our aim was to investigate the efficacy, toxicity, and drug discontinuation in patients with ankylosing spondylitis (AS) treated with infliximab. Thirty-five patients with AS, who were enrolled between June 2001 and December 2002 were treated with infliximab. All patients fulfilled the New York revised criteria for AS and had axial disease. Infliximab (5 mg/kg weight), was given intravenously at weeks 0, 2, 6, and every 8 weeks thereafter. If this failed to give an acceptable treatment response, the interval was shortened to 6 or 4 weeks. The patients were followed-up at predefined times according to a standardized protocol. Data concerning infliximab efficacy, tolerability, adverse events, interval, and drug discontinuation were all recorded. Clinical improvement according to the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) 50% and the Ankylosing Spondylitis Assessment Study group (ASAS) 40%, and ASAS 5/6 response criteria were recorded. Infliximab treatment resulted in a rapid improvement in the BASDAI and ASAS scores in the first year of the treatment, which sustained throughout the fourth year. More specifically, after the third year of treatment 17/35 (48.6%) of patients achieved BASDAI 50% response criteria, 19/35 (54.3%) attained the ASAS 40% and 15/35 (42.9%) reached the ASAS 5/6. After the fourth year of treatment BASDAI 50% was reached by 17/35 (48.6%) of patients, ASAS 40% by 17/35 (48.6%), while ASAS 5/6 was attained by 15/35 (42.9%). The clinical improvement was associated with the reduction of acute phase reactants as measured by C-reactive protein levels. After the first year of treatment, the "survival rate" of infliximab was 94.3%, after the second year was 91.4%, after the third year was 85.7% and even after 4 years of treatment still maintained high 77.9%. Six (17.1%) patients were withdrawn during the observational period. Three because of lack of efficacy, two because of allergic reactions and one lost from follow-up. Infliximab was effective, safe, and well tolerated in patients with AS. The clinical response was maintained for a period of 4 years and over, with infliximab survival of 77.9%.