The invention relates to a control valve (10) for a fuel injector (100) for internal combustion engines, which control valve comprises a valve piece (11), which has a valve seat (12) and a valve closing armature (20), which interacts with the valve seat (12) and can be moved in a reciprocating manner. A discharge bore (30) having a circular cross-section is formed in the valve piece (11). The discharge bore comprises a first region having a diameter d
1 , which first region serves as a throttle (31), a second region, which serves as a diffuser (32), and a third region having a diameter d
3 , which third region serves as a following flow geometry (33). The second region has at least one segment having a diameter d
2 , and the following applies: d
1 2 3 . The third region B
3 serving as a following flow geometry (33) has a length l
3 , wherein the following applies to the ratio l
3 /d
3 : 2 3 /d
3 3 /d
3 preferably being approximately equal to 2.5.