In this work, the influence of track density and chemical etching on the reproducibility of the track counting efficiency, ε0, in solid state nuclear track detectors (SSNTDs) is studied. This was performed by means of the analysis of CR-39 sheets that were attached to a thin film of natural uranium. Maintaining the chemical etching parameters constant and varying the exposition time, ε0 is observed to be constant for track densities varying between values approximately equal to the track background and those corresponding to the track overlapping limit, where track counting becomes difficult ( ∼ 105 cm-2 at our conditions). Otherwise, keeping constant the exposition time and varying the etching temperature, a variation in ε0 is found if a usual track counting criterion is employed. However, such a variation vanishes statistically when a more rigorous criterion is adopted. © 1998 Elsevier Science B.V. All rights reserved.