Introduction and Objectives: Which ureteral stone can pass spontaneously? It is hard to answer this question exactly. The size and location of the stone are the most important predictors. However, there is still a considerable gray zone that needs to be clarified. We try to identify the role of stone volume (SV) in the prediction of spontaneous passage (SP). Materials and Methods: Seventy-eight patients with a solitary ureteral stone were retrospectively evaluated. Ureter SV measurements were taken in three planes and were calculated using the following formula: V=(X)x(Y)x(Z)x0.52. SVs, and the longest diameters (LDs) were compared between patients who passed stones spontaneously and those who needed intervention. Results: The SVs and LDs were significantly lower in patients who passed stones spontaneously than in patients who required intervention (41.235.5 vs 128.1 +/- 91.1mm(3), p=0.001; 5.7 +/- 1.8 vs 7.4 +/- 1.7mm, p=0.001). The optimum cutoff values were 7.0mm and 52.6mm(3) for the LD and SV, respectively. For those stones of 7mm, the volumes of the stones that could and could not pass did not differ significantly. However, the volume of the stones >7.0mm that could pass was significantly higher than of those that could not. SP was 30.6% for stones >7mm; however, when we removed the stones >52.6mm(3), SP increased to 75% for stones higher than 7mm (p=0.001). Conclusions: To classify ureteral stones using only one parameter such as stone diameter may lead to heterogeneity within the group. SV may be used in addition to size to determine a more definite homogeneous group to predict SP more precisely.