Purpose: Despite the recent success of mechanical thrombectomy (MT) in the treatment of acute ischemic stroke, prognostic parameters and criteria for patient selection are yet uncertain. Elevated levels of white blood cells (WBCs) constitute an independent risk factor for unfavorable outcome. Here we studied the link between outcome and WBC counts obtained before and after successful MT. Methods: One hundred fifteen acute stroke patients successfully treated with MT (thrombolysis in cerebral infarction-scores 2b or 3) were included. WBC counts and C-reactive protein (CRP) levels were obtained prior to (WBC-pre, CRP-pre) and 1 day after MT (WBC-post, CRP-post). Clinical outcome measures consisted of National Institute of Health Stroke Scale (NIHSS) scores, and modified Rankin Scale (mRS) on day 90 (mRS-d90), dichotomized between scores ≤5 and >5 (NIHSS) and ≤2 and >2 (mRS). The association between WBC-/CRP-levels and outcome was assessed by correlation- and receiver-operating characteristic analyses. Results: WBC counts on day 1 after MT correlated significantly with NIHSS scores at discharge and mRS-d90. Among patients >50 years, no patient with WBC-post counts exceeding 14.2 G/l had favorable NIHSS scores (≤5), and no one with WBC-post counts ≥12.6 G/l had favorable mRS-d90 outcome-scores (≤2). Further, even WBC-pre counts ≥10.6 G/l predicted unfavorable mRS-d90-scores in this subgroup. Conclusion: Elevated WBC counts obtained in routine blood tests may constitute a simple and economic parameter to estimate outcome after successful MT. Moreover, present data suggest that in patients older than 50 years, WBC counts may help to predict outcome even when obtained prior to MT.