Purpose. The present study investigated inter-software variability in automatically detected seed location and dose volume histogram (DVH). Materials and methods. Image sets from computed tomography (CT) of 25 patients treated using interstitial permanent brachytherapy were examined. Interplant and Variseed were used as software for post-implanted CT analysis. Seed locations are automatically detected by Variseed and Interplant. Dose-volume histograms were calculated using seed locations as detected by the two programs. DVH parameters were compared between Variseed and Interplant. Results. Considerable differences in DVH parameters existed between Variseed and Interplant. For example, mean differences in dose to 90% of prostate volume (pD90) and dose to 5% of urethral volume (uD5) were 8.27 Gy and 20.18 Gy, respectively. The difference in uD5 was associated with prostate volume. Conclusion. Our results suggest that considerable inter-software variability exists in post-implanted CT analysis. DVH parameters from other software should be used with care.