In spite of the high prevalence of advanced colorectal cancer in the elderly, we have little data on the efficacy and toxicity of chemotherapy in this age group. Raltitrexed is a thymidylate synthetase inhibitor with known activity in the treatment of advanced colorectal cancer. The objective of this study was to analyse the efficacy and tolerance of raltitrexed in elderly patients with advanced colorectal cancer. 92 patients diagnosed with advanced colorectal cancer aged >or=70 years were entered into the study. Raltitrexed was given at a dose of 3 mg/m(2) once every 3 weeks for a minimum of three cycles. A total of 511 cycles were given with a median of five cycles per patient. 20 out of the 90 patients evaluable for response achieved a partial response (PR) (22%, 95% Confidence Interval (CI): 17-36%), 43 (48%) remained stable and 27 showed progression (30%). The mean duration of response was 24 weeks and the progression-free interval was 15 weeks. The overall median survival was 41 weeks. 31 patients (39%, 95% CI: 28-50%) experienced a clinical benefit (improvement of the performance status without a worsening of symptoms or relief of symptoms without a worsening of the performance status). The main toxicities were gastrointestinal and haematological. 12 patients (13%) developed grade 3-4 side-effects: 7 had nausea/vomiting (8%), 6 a transaminase increase (7%), 4 asthenia (4%), 3 diarrhoea (3%), 2 neutropenia (2%), 2 anaemia (2%) and 1 thrombocytopenia (1%). Three toxic deaths occurred (3%). The group of patients with a creatinine clearance <or=1.08 ml/s was found to have a higher risk of developing grade 3-4 toxicity compared with those with adequate renal function (8/18 versus 4/72; P<0.001). In conclusion, raltitrexed is an active, convenient and low toxicity treatment for the elderly with advanced colorectal cancer. However, it must be used cautiously in elderly patients with a creatinine clearance <or=1.08 ml/s since they are at a higher risk of suffering grade 3-4 toxicity.