Objectives - To investigate the clinical effectiveness and cost-effectiveness of laxatives versus dietary and lifestyle advice, and standardised versus personalised dietary and lifestyle advice. Design - A prospective, pragmatic, three-armed cluster randomised trial with an economic evaluation. Setting: General practices in England and Scotland, UK. Participants - People aged ? 55 years with chronic constipation, living in private households. Participants were identified as those who had been prescribed laxatives three or more times in the previous 12 months, or with a recorded diagnosis of chronic functional constipation. Interventions - Prescription of laxatives, with class of laxative and dose at the discretion of the GP and patient (standard care control arm); standardised, non-personalised dietary and lifestyle advice; and, personalised dietary and lifestyle advice, with reinforcement. Outcome measures - The primary outcome was the constipation-specific Patient Assessment of Constipation-Symptoms (PAC-SYM)/Patient Assessment of Constipation-Quality of Life (PACQOL). Results - The trial planned to recruit and retain 1425 patients from 57 practices (19 per arm); however, only 154 patients were recruited from 19 practices. Due to these low recruitment rates it was not possible to report the conventional trial findings. Baseline characteristics of the sample from data gathered from both postal self-completion questionnaires and face-to-face interviews suggest that our sample experienced very few symptoms of constipation (PAC-SYM) and that the condition itself did not have a major impact upon their quality of life (PACQOL). The low level of symptoms of constipation is most likely explained by 90% of the sample using a laxative in the previous week. Most participants in our sample were satisfied with the performance of their laxatives, and levels of anxiety and depression were low. Their fibre consumption was classified as ‘moderate’ but their average water consumption fell below the recommended guidelines. Daily diaries, completed each day for a period of 6 months, were analysed primarily in terms of overall response rate and item response rates, and the participants accepted this method of data collection. For the economic evaluation, all of the trial arms experienced a reduction in utility, as measured by EQ-5D. There was no statistical evidence to suggest that either the personalised intervention arm or the standardised intervention arm was associated with significant changes in utility at 3 months compared with the control arm. Data on related health-care costs show a cost saving of £13.34 for those in the personalised arm, compared with the control arm, and a smaller cost saving for the standardised arm. These savings primarily occurred because of reduced hospital costs. There was no significant change measured in utility, so the personalised arm appeared to be the preferred course, producing the greatest cost savings. Conclusions - Due to the low number of participants in the trial, no firm conclusions could be drawn about the effectiveness of the interventions. However, a number of factors that contributed to the conduct and progress of the trial are highlighted, which may be relevant to others conducting research on a similar topic or population. Trial registration: ISRCTN73881345. Funding: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 14, No. 52. See the HTA programme website for further project information.