The literature concerning serous borderline tumors with a noninvasive micropapillary component suggests an association with invasive implants. We compared the clinicopathologic features of micropapillary serous borderline tumors (MSBTs) with typical SBTs to determine the following: 1) the importance of focal micropapillary architecture in an otherwise typical SBT, 2) the behavior of low-stage MSBTs, 3) whether high-stage MSBTs are inherently more aggressive than high-stage SBTs, and 4) whether invasive implants are prevalent in an MSBT cohort without referral selection bias. The 57 borderline tumors studied were diagnosed at a university hospital between 1981 and 1998; they included 14 MSBTs, 35 SBTs, and 8 SBTs with focal micropapillary features. None of the specimens were referrals for expert pathologic consultation, thus distinguishing our study group from most of those previously reported. Neither MSBTs nor SBTs were associated with invasive implants at diagnosis (0 of 14 and 0 of 43, respectively). They also did not differ with respect to overall stage at diagnosis, but MSBTs were more frequently bilateral than SBTs (71% versus 23%, p = 0.001). There was an increased risk of recurrence in MSBT versus SBT (3 of 14 versus 1 of 43, p = 0.035), but this was stage related; there was no difference between groups when evaluating recurrence in stage I disease (0 of 8 versus 0 of 27). There was no difference in recurrence or stage at diagnosis between SBTs with focal micropapillary features and other SBTs. There was 100% survival in all groups. We conclude that high-stage MSBTs with noninvasive implants should be considered a subtype of SBTs with an increased risk of recurrence. Stage I MSBTs demonstrate clinical features that are similar to low-stage SBTs. Focal micropapillary architecture (<5 mm) has no bearing on outcome. MSBTs in the general population are not strongly associated with invasive implants.