A dietary assessment website for use in the primary healthcare setting has been developed. The website allows patients, referred from their GP, to self-report their dietary intake. Data from the website feeds to a dietitian who develops individualised dietary advice for the patient. The aim of this paper is to describe the usability testing of the dietary assessment website with its potential users. Testing was broken into two phases. Forty-two free-living adults with metabolic syndrome volunteered, 17 completed phase one and 10 completed phase two, with a 64% rate of completion. Phase one participants spoke aloud as they progressed through the self-administered dietary assessment website under researcher observation. Observed difficulties in website use and need for assistance was recorded and the website underwent modifications between phases. Only four participants in phase 1 required large amounts of assistance. Phase two participants progressed through the website without observation or using the think-aloud protocol. This simulated the environment in the GP practice within which the website was to be implemented. All participants completed pre- and post-use questionnaires assessing feelings toward use, computer experience and problems encountered. Questionnaires were thematically analysed for relationships between website use and participant feelings. Time taken to use the website was recorded automatically. Website features were grouped into 'action classes' e.g. selecting food items, and times taken were calculated for each class. Comparisons (t-tests) were made between the action classes for the two phases. Average time taken to select the food items was 31mins and 24mins for phase one and two respectively. Total time taken was approximately 1 hour and varied by four minutes between phases. Time taken to complete the dietary assessment was comparable to a face-to-face diet history with a dietitian. The website was found to be highly user-friendly with little assistance being required for most levels of computer experience. Dietary management may be overlooked by GPs, yet by offering different methods of accessing dietitians, management may improve.