West syndrome or infantile spasms is one of the most frequent epileptic syndromes in the first year of life. The clinical symptoms of infantile spasms are very different than any other type of seizure because of both the absence of paroxysmal motor phenomena (i.e., as in a convulsion) and the lack of significant duration of loss of consciousness (i.e., as in absence epilepsy). Infantile spasms may lead to misdiagnosis by pediatricians and other primary care providers. We assessed the missed diagnoses prior to the diagnosis of infantile spasms. We hypothesized that a delay in treatment may have consequences on neurologic outcome. We conducted a multicenter, retrospective, observational study to evaluate occurrence of misdiagnosis and its possible consequences. We performed a multivariate analysis to evaluate the risk for the outcome 2 years after the diagnosis of infantile spasms. We included 83 infants over a 5-year period. The majority of consulted physicians (301 of 362) did not suggest any specific diagnosis while the others suggested gastroesophageal reflux (7 %), constipation (7 %), or colitis (3 %). Results indicated that a poor outcome was related to a delay in diagnosis, which was observed regardless of the existence of cognitive involvement prior to the start of infantile spasms (Relative Risk: RR 12.08 [1.52-96.3]). These results highlight the importance of making an early diagnosis of infantile spasms.