The 1999 NIST Speaker Recognition Evaluation encompassed three tasks: one-speaker detection, two-speaker detection, and speaker tracking. All tasks were performed in the context of conversational telephone speech. The one-speaker task used single channel mu-law data; the other tasks used summed two-channel data. Twelve sites from the United States, Europe, and India participated in the evaluation. Performance was measured by a decision cost function and compared among systems and test conditions via DET Curves. Performance factors examined include segment duration, degradation resulting from the presence of a second speaker, sex mix of the two-speaker segments, matched or mismatched between training and test handsets, and the variation in handset type.