The results of CT were studied prospectively in 606 patients with a transient ischaemic attack (TIA), 422 patients with a reversible ischaemic neurological deficit (RIND), and 1054 patients with a minor stroke, were all entered into a multi-centre clinical trial. CT scanning showed a relevant ischaemic lesion in 13% (95% confidence interval 10-16%) of TIAs, 35% (95% confidence interval 30-40%) of RINDs, and 49% (95% confidence interval 46-52%) of minor strokes (p less than 0.000001). Even within the 24 hour margin, relevant infarcts occurred more often with longer attacks, but were still found in some patients with attacks lasting less than a minute. The type and location of the infarcts were similar in the three groups. These findings suggest that the differences between TIAs, RINDs, and minor strokes are quantitative rather than qualitative.