In this paper, investigation of position sensitive avalanche photodiodes (PSAPDs) as optical detectors for reading out segmented scintillation arrays of LSO in high resolution PET modules is reported. PSAPDs with 8 x 8 mm(2) and 14 x 14 Turn 2 area have been characterized with single LSO crystals and arrays. Energy resolution of 19% (FWHM) for 511 keV gamma-rays and coincidence timing resolution of similar to3 ns (FWHM) have been recorded with PSAPD coupled to 1 x I x 20 mm(3) LSO detectors. Flood histogram studies have been successfully conducted by coupling multi-element element LSO arrays (1 mm pixels, 20 mm tall) to the PSAPDs. Finally, depth of interaction (DOI) resolution of <4.5 mm (FWHM) has been measured by coupling two PSAPDs on opposite ends of a 20 mm long LSO crystal with a I X 1 mm(2) cross section. Based on these results, PSAPDs appear to be promising for high resolution PET. An important advantage. of these PSAPDs is significant reduction in electronic readout requirements.