We use the VENUS-3 experimental benchmark to examine the accuracy and parallel performance of PENTRAN™ (Parallel Environment Neutral-particle TRANsport), a three- dimensional parallel Sn code. VENUS-3 with its partial length assemblies is a 3-D benchmark with 370 measurements (⁵⁸Ni(n,p), ¹¹⁵In(n,n'), and ²⁷Al(n,α) dosimeters). PENTRAN results are very close to experimental results; more than 95% of the Calculated-to-experimental (C/E) values are within ±10%. The remaining 5% of the values are within ±10% and ±15%. The PENTRAN calculation (with 84748 spatial meshes, 80 directions, and 26 energy groups) is performed on an IBM SP2 parallel computer using different numbers of processors and different parallel algorithms. It is demonstrated that PENTRAN requires less than 1.4 hrs wall-clock time on32 processors, and it exhibits an excellent parallel performance with a scalability of ̃90%.