| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Jarmila | - | Czech, Slovak | ||
| Jaroslav | - | Czech, Slovak | ||
| Jaroslava | - | Czech, Slovak | ||
| Jela | - | Serbian, Croatian, Slovak | ||
| Jolana | - | Czech, Slovak | ||
| JonÁŠ | - | Czech, Slovak | ||
| Jozef | YO-zəf (Dutch) | Slovak, Dutch | ||
| JozefÍNa | - | Slovak | ||
| Judita | - | Lithuanian, Czech, Slovak | ||
| Juraj | YOO-rahy (Croatian) | Croatian, Slovak | ||
| JustÍNa | - | Slovak | ||
| KajetÁN | - | Czech, Slovak, Hungarian | ||
| Kamil (2) | KAH-meel (Polish) | Czech, Slovak, Polish | ||
| Kamila | kah-MI-lah (Czech, Slovak), kah-MEE-lah (Polish) | Czech, Slovak, Polish | ||
| Karol | KAH-rawl (Polish) | Polish, Slovak, Slovene |