Modern treatment in childhood acute lymphoblastic leukemia (ALL) resulted in high cure rate. However, it causes central nervous system toxicity. A group of 136 ALL survivors were screened for P300 potentials changes. Therapy was conducted according to modified New York (NY - 30 patients) and two subsequent revisions of modified Berlin-Frankfurt-Münster (BFM - 32 and 74 patients). The control group consisted of 58 patients. The survivors had significantly prolonged the mean latency of P300 (331.31+/-28.71 vs 298.14+/-38.76 ms, P<0.001) and reaction time (439.51+/-119.86 vs 380.11+/-79.94 ms, P=0.002) compared to the control group. Abnormalities in the endogenous evoked potentials were observed in 36 patients (26,5%). The mean latency time was significantly longer compared to the control group (NY: 329.13+/-28.07 ms, P=0.001; pBFM: 332.97+/-23.97 ms, P<0.001; BFM95: 331.47+/-31.05 ms, P<0.001). The reaction time was similarly prolonged in both groups. The most significant prolongation was recorded in the NY group (461.8+/-140.3 vs 380.1+/-78.04 ms, P=0.039). Significantly higher frequency of prolonged reaction time in non-irradiated BFM95 patients was found (21.62 vs 15.85%, P=0.007). Radiotherapy have significantly reduced the P300 wave amplitude (mean values: 10.395+/-5.727 vs 12.739+/-6.508 ms, P=0.027). Endogenous P300 event-related potentials may be useful in screening of subclinical cognitive changes in ALL survivors.