The performance of the position sensitive detector for the ZEBRA low energy gamma-ray imaging telescope is described. The detector consists of 9 position sensitive Nal(TI) elements each 5.8 × 5.0 × 56.0 cm viewed at either end of the long axis by 2 in. photomultiplier tubes. The total active area is 2470 cm2 with an average positional resolution of 2.1 cm and energy resolution of 15% FWHM at 661.6 keV. The method of flight calibration is described together with the provision within the on-board electronics to correct for sources of error in the calculation of event energy loss and position. The results presented are obtained from the calibration phase of the ZEBRA telescope project.