['The need for routine medical examinations of sport divers in the Scottish Sub-Aqua Club (Scot-SAC) was revised in March 2000, and a new system using a self administered screening questionnaire was developed to allow divers to be assessed when necessary by doctors with diving medicine experience.', 'To assess the effect of the new medical system on medical referee workload, diver exclusion rates, and diving incident frequency.', 'All divers were required to complete a questionnaire to screen for conditions that might affect fitness to dive. Divers answering "Yes" to any of the questions had their medical background assessed by a diving doctor, and, if necessary, received a clinical examination or investigation. The rate of diver exclusions based on the questionnaire response was recorded in conjunction with analysis of the incident reports.', 'The number of forms requiring review by diving doctors increased from 1.2% to 5.7% (p<0.0001, 95% confidence interval (CI) -0.06 to -0.03) in the year after the introduction of the new medical system and gradually increased in subsequent years to 7.7% (p<0.0001, 95% CI -0.08 to -0.05). The number of divers failing to be certified fit to dive increased slightly from 0.7% to 1.0% after one year (p = 0.26, 95% CI -0.01 to 0.00) and subsequently to 2.0% (p = 0.0003, 95% CI 0.02 to -0.01) after three years. Most divers were certified fit to dive on the basis of the questionnaire alone, and only 0.9% required objective investigation (such as exercise testing or echocardiography). Analysis of the incidents during three years of follow up confirmed that no incident occurred because of an undetected pre-existing medical condition. Two incidents involved divers with hypertension, but both had received medical examinations and investigation based on their responses to the questionnaire.'] Do three year follow up of a self certification system for the assessment of fitness to dive in Scotland?