Previous studies with small numbers of clutches suggested that Pied Flycatchers (Ficedula hypoleuca) were determinate egg-layers whose clutch size was fixed before laying began. We found that females lay additional eggs of normal size if clutch size is experimentally reduced, but do not lay fewer eggs when clutch size is increased. In the terms of Kennedy and Power (1990), Pied Flycatchers are removal-indeterminate and addition-determinate.