The objective of this study was to optimize protocols for the cryopreservation of sex-sorted boar spermatozoa. In the experiment 1, we evaluated the effects of a standard boar sperm cryopreservation procedure (3% final glycerol concentration) on the in vitro characteristics of sex-sorted sperm frozen at low sperm concentrations (20 x 10(6) sperm/ml; S20 group). Non-sorted spermatozoa frozen at 1000 x 10(6) (C1000 group) and 20 x 10(6) (C20 group) sperm/ml were used as the freezing control groups. In experiment 2, the effects of different final glycerol concentrations (0.16%, 0.5%, 1.0%, 2.0% and 3.0%) on post-thaw quality of the S20 and C20 groups were evaluated. In both experiments, the samples were evaluated prior to freezing (5 degrees C) and at 30, 90 and 150 min after thawing. Experiment 1 indicated that freezing sperm at low concentrations decreased (p < 0.05) the total motility (TM) and progressive motility (PM) at 90 and 150 min after thawing regardless of whether the sperm were sorted or not. However, the sperm membrane integrity was not affected at any evaluation step. Inexperiment 2, significant effects on the TM and PM because of increased glycerol concentrations in the S20 and C20 groups were observed only at 90 and 150 min after thawing. The samples frozen in 3% glycerol showed lower (p < 0.05) TM and PM values when compared to those frozen in the presence of 0.5% and 1% glycerol. In both experiments, non-sorted control samples displayed higher percentages of spermatozoa with damaged DNA than sorted spermatozoa. In conclusion, the optimization of cryopreservation conditions by decreasing the glycerol concentrations can improve post-thaw motility of sex-sorted spermatozoa frozen at low concentrations.