<b><i>Background and Purpose:</i></b> Early neurological deterioration (END) occurs in 10-40% of acute ischemic stroke (AIS) patients and has been associated with worse outcome. Recent improvements in treatment may have reduced the prevalence of END. A single early control or repeated observations have been applied to detect END close to occurrence, in order to improve the poor outcome associated with END, as clinical interventions may still be effective. Deterioration detected through repeated observations may be transitory or lead to END. Our aim was to study outcome after END and transitory deterioration (TD). <b><i>Methods:</i></b> In acute ischemic stroke patients, key Scandinavian Stroke Scale (SSS) items were scored 12 times from admission to 72 h. END was defined as ≥2 point decrease in any key SSS item from admission to 72 h. Early deterioration episode was defined as similar worsening between two consecutive assessments within 72 h, and TD as early deterioration episode in patients without END. Main outcome measures were odds ratios (OR) for worse functional outcome (including death) measured by modified Rankin scale at 90 days for END and TD compared with stable patients. <b><i>Results:</i></b> 368 patients were included. 13.9% had END and 28.3% had TD. Both deterioration groups were associated with worse outcome at 12 weeks compared with stable patients, with ORs of 35.1 (95% CI 8.8-140) for death/dependency and 5.8 (95% CI 1.8-19.4) for death in END patients and ORs of 2.3 (95% CI 1.1-4.8) for death/dependency and 1.9 (95% CI 0.5-6.3) for death in patients with TD. LOS increased by 6.4 days for END (p < 0.001) and 1.1 days for TD (p = 0.014) compared with stable patients. <b><i>Conclusion:</i></b> We found a strong association between END and worse outcome, and even TD doubled the OR for death/dependency compared to stable patients. Early deterioration episodes identified through frequent observations are therefore clinically significant and such frequent observations may detect worsening sufficiently close to occurrence for potentially effective treatment to be applied.