The efferent connections of different cytoarchitectonic areas of the superior temporal sulcus (STS) in the rhesus monkey with parieto-temporo-occipital cortex were investigated using autoradiographic methods. Four rostral-to-caudal subdivisions of cortex (area TPO) in the upper bank of the STS have distinct projection patterns. Rostral sectors (areas TPO-1 and -2) project to the rostral superior temporal gyrus (areas Ts1, Ts2, and Ts3), insula of the Sylvian fissure, and parahippocampal gyrus (perirhinal and prorhinal cortexes, areas TF, TH, and TL); caudal sectors (TPO-3 and -4) project to the caudal superior temporal gyrus (areas paAlt and Tpt), supratemporal plane (area paAc), circular sulcus of the Sylvian fissure (area reIt), as well as medial paralimbic (areas 23, 24, and retrosplenial cortex) and extrastriate (areas 18 and 19) cortexes. Area TPO-1 does not project to the parietal lobe; area TPO-2 projects to the inferior parietal lobule; area TPO-3 to the lower bank of the intraparietal sulcus (IPS) (area POa); and area TPO-4 to medial parietal cortex (area PGm). Vision-related cortex (area TEa) in the rostral lower bank of the STS sends fibers to the rostral inferotemporal region (areas TE1, -2, and -3) and parahippocampal gyrus (perirhinal cortex, areas TF and TL). Visual zones in the caudal lower bank and depth of the sulcus (area OAa, or MT and FST) project to the caudal inferotemporal region (areas TE3 and TEO), lateral preoccipital region (area V4), and lower bank of the IPS (area POa). A zone in the rostral depth of the STS (area IPa) projects to the rostral inferotemporal region, parahippocampal gyrus, insula of the Sylvian fissure, parietal operculum, and lower rim of the IPS (area PG). STS projections to parieto-temporo-occipital cortex have "feedforward," "feedbackward," and "side-to-side" laminar patterns of termination similar to those of other cortical sensory systems. The differential connectivity supports the cytoarchitectonic parcellation of the STS and suggests functional heterogeneity.