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PURPOSE To determine the prognostic value of visually detected coronary artery calcification (CAC) on unenhanced non-gated thoracic computed tomography (CT) for non-fatal myocardial infarction (MI) and all-cause mortality. METHODS This retrospective single-centre cohort study comprised of 410 consecutive patients aged 40-80 years without any known cardiovascular disease at baseline. CT images without electrocardiogram-gating were acquired for a variety of respiratory medicine indications. CAC was examined by a single reader blinded to clinical data and outcome, using 1) the Agatston coronary calcium score (CCS), 2) visual CAC and 3) number of visually calcified coronary arteries. RESULTS Visible CAC was identified in 201 (49.0%) of the 410 patients (60.5 ± 10.0 years old, 42.4% males). After a median follow up of 7.0 years, 39 patients (9.5%) experienced an event (death or non-fatal MI). After adjustment for cardiovascular risk factors, those with 1) higher CCS, 2) presence of visual CAC or 3) greater number of calcified coronary arteries by visual assessment, had an increased risk of adverse outcome (all p-value <0.05). There was no significant difference in c-statistics of the three methods of assessment (0.81, 0.80, 0.81 respectively), indicating that simple visual assessment of CAC may have a prognostic value similar to CCS. CONCLUSION Among patients with no known cardiovascular disease who underwent unenhanced non-gated CT for a pulmonary-related indication, visually detected CAC was a strong independent predictor of non-fatal MI and all-cause mortality.