The task of monitoring the Earth for nuclear explosions relies heavily on seismic data to detect, locate, and characterize suspected nuclear tests. Motivated by the need to locate suspected explosions as accurately and precisely as possible, we developed a tomographic model of the compressional wave slowness in the Earth’s mantle with primary focus on the accuracy and precision of travel‐time predictions for P and Pn ray paths through the model. Path‐dependent travel‐time prediction uncertainties are obtained by computing the full 3D model covariance matrix and then integrating slowness variance and covariance along ray paths from source to receiver. Path‐dependent travel‐time prediction uncertainties reflect the amount of seismic data that was used in tomography with very low values for paths represented by abundant data in the tomographic data set and very high values for paths through portions of the model that were poorly sampled by the tomography data set. The pattern of travel‐time prediction uncertainty is a direct result of the off‐diagonal terms of the model covariance matrix and underscores the importance of incorporating the full model covariance matrix in the determination of travel‐time prediction uncertainty. The computed pattern of uncertainty differs significantly from that of 1D distance‐dependent travel‐time uncertainties computed using traditional methods, which are only appropriate for use with travel times computed through 1D velocity models.