The objective of this study was to assess the value of quantitative HIV-1 RNA as a predictor for the short-term risk of developing AIDS-defining events in comparison with CD4 cell counts. A total of 1,028 samples from 324 patients were analysed. Median initial CD4 cell counts and HIV-1 RNA were 249 x 10(6)/l (range 0-1400 x 10(6)/l) and 4.5 log copies/ml (range: 2.3-6.4 log copies/ml). CD4 cell counts and viral load (VL) values obtained the year before a single AIDS-indicator disease were selected to define the risk of developing that event. Cox regression models with CD4 cell counts and VL values treated as time-dependent covariates were performed to analyse the risk for developing certain events. Receiver operating characteristic (ROC) curves were used to compare CD4 cell counts and VL values as predictive markers for progression. During a median follow-up of 870 d (range 30-1381 d), 132 patients developed AIDS. Median log VL values during the year before the event were 3.6 for non-progressors and 5.2 for those who developed AIDS (p < 0.0001). Minimum log VL threshold values for developing diseases were 2.3 for tuberculosis, 3.8 for Candida esophagitis, 4.4 for wasting syndrome, 4.5 for CMV disease and 4.7 for PCP. VL values were not, however, a better predictive marker for developing specific events than were CD4 cell counts. Although we have identified VL thresholds for the risk of developing certain AIDS-indicator diseases, the indication for starting prophylactic regimens may still be based on CD4 cell counts.