1998–99 LEN Champions League
The 1998–99 LEN Champions League was the 36th edition of LEN's premier competition for men's water polo clubs. It ran from 1998 to 5 June 1999, and it was contested by 16 teams. The Final Four took place on June 4 and June 5 in Naples.
Preliminary round
| Key to colors in group tables |
| Group winners and runners-up advanced to [|Final four] |
Final Four ([Naples])
Final standings
| Team | |
 |