We aimed to characterize and to explore a treatment for a condition in which male mice exhibited a solid bulge in the preputial area and an inability to breed. Twenty-seven mice from several animal housing institutions in Spain were included in this study for microbiological and pathological characterization of this condition. The condition mostly affected breeding animals and was associated with the C57BL/6J genetic background. A solid, yellowish-white substance was found inside the prepuce, which displaced the penis cranially, preventing its externalization and limiting the animal's capacity to breed. This pattern was almost identical to that of post-coital vaginal plugs, suggesting that the blocking substance originated from ejaculate. Opposite to what was suggested in previous publications, the penis was completely intact in all of the cases, with no signs of mutilation or wounds. Based on our findings, we developed a surgical technique to clear the prepuce and recover breeding performance, which we tested in 15 other mice with the condition. We eliminated the blocking substance and recurrence of the condition by surgically opening the prepuce, and most of the animals recovered fertility.