Edwards-Brown v. Crete-Monee 201 U School Dist., 2012 U.S. App. LEXIS 16358 (7th Cir. Aug. 7, 2012):

We note first that the district court properly construed Brown's "motion" for voluntary dismissal as a notice of voluntary dismissal under Rule 41(a)(1). That she incorrectly called it a "motion to dismiss" is irrelevant. See Smith v. Potter, 513 F.3d 781, 783 (7th Cir. 2008) (holding that a "motion to voluntarily dismiss the plaintiff's complaint" was, despite its title, actually a Rule 41(a)(1) notice of dismissal). A voluntary dismissal filed before any responsive pleading is filed is self-executing and automatically effects dismissal of the case. See id. at 782 ("The miscaptioned motion itself effected the dismissal of the suit; the case was gone; no action remained for the district judge to take."). The defendants had moved to dismiss under Rule 12(b)(6), but a motion to dismiss is not a responsive pleading. Duda v. Bd. of Educ. of Franklin Park Pub. Sch. Dist. No. 84, 133 F.3d 1054, 1056 n.2 (7th Cir. 1998). The dismissal of Brown's suit was therefore effective on October 26, 2009, the date on which she filed the "motion" for voluntary dismissal--not on November 17, 2009, the date on which the court issued the superfluous order "granting" the motion.

Voluntary dismissal under Rule 41(a)(1) generally means the suit is treated as if it was never filed in the first place, but there are exceptions to this rule, and dismissal "does not deprive a district court of jurisdiction for all purposes." Nelson, 657 F.3d at 589. For example, courts may consider collateral questions, such as Rule 11 sanctions or criminal contempt charges, even after the original suit is voluntarily dismissed. See Cooter & Gell v. Hartmarx Corp., 496 U.S. 384, 395-96 (1990). We have also stated that "there may be instances where a district court may grant relief under Rule 60(b) to a plaintiff who has voluntarily dismissed the action," Nelson, 657 F.3d at 589--assuming, of course, that a proper basis under Rule 60(b) is present.