The determination of lesion volumes in acute cerebral Infarction (CI) has important prognostic and therapeutic implications. Three different methods -computerised technique, linear planimetry and the A.B.C/2 formula - were compared in 27 patients using non-contrast computerised tomography (CT) made at hospital admission (first 48 hours following symptom onset). Two independent observers performed the measurements. The Intra-class correlation coefficients (ICCs) were determined. The three methods exhibited high interrelation. There was a close correlation between the linear planimetry as well as the ABC/2 formula and the computerised method with ICCs of 0.94-0.95 and 0.835-0.90 respectively. Linear planimetry and the ABC/2 formula were also highly correlated, with ICCs between 0.97 and 0.99. In conclusion, the computerised method is probably the most accurate. Linear planimetry and the ABC/2 formula are also reliable, however. The A.B.C/2 formula should be applied routinely to CI volume determination based on its low cost and fast calculation.