It is desirable to have an accurate method to determine the depth of various organs which are commonly imaged in nuclear medicine. The method presented here utilizes the geometrical characteristics of the rotating slant-hole collimator to calculate distances and depth. The accuracy of the calculated distance was evaluated for point sources in air separated by 11 cm. The reproducibility of the calculated distance was evaluated as a function of the extent of collimator rotation between observations for angular differences of 45 degrees, 90 degrees, 135 degrees, and 180 degrees. The theory of the method is discussed and the relative error in distance calculation analyzed mathematically as a function of (1) collimator rotation angle error, (2) collimator slant angle error, and (3) position calculation error. Our findings indicate this method to be accurate to within 2% with a reproducibility range of 3%-5% for point sources.