OBJECTIVE Our purpose was to compare the clinical experience in using Dilapan osmotic dilator and Laminaria japonicum as overnight osmotic cervical dilators in second-trimester dilation and evacuation abortion with respect to measurable outcome variables, including complication rates. METHODS A cohort comparison was performed of 1001 patients receiving alternate preoperative treatment with either osmotic dilator after initial randomization until this number had been reached in the series. RESULTS Few significant differences were found in the two cohorts with respect to blood loss, procedure times, and overall complication rates. However, patients receiving the Dilapan dilator were at least twice as likely to experience problems in cervical dilation or problems resulting from poor dilation or disintegration of the device than were patients receiving Laminaria japonicum. Although more patients receiving laminaria experienced amniotic fluid embolism or disseminated intravascular coagulation syndrome, these problems could not be attributed to the type of osmotic dilator used. CONCLUSIONS Both osmotic dilators are acceptable for use in overnight dilation in this procedure, but the Dilapan dilator is more likely to disintegrate, retract, or present minor problems associated with poor dilation.