Background: Children with Down syndrome frequently develop infantile spasms (IS); however, variable seizure outcome has been reported and not much is known about the clinical-electrophysiological factors affecting these outcomes. Therefore, we evaluated the clinical, neuroimaging and electrophysiological data in our DS with IS patient cohort, with a relatively long follow-up duration, to address some of these issues.  Methods: Disease characteristics, diagnostic tests and treatment outcomes from 15 children (F: M=7:8) with IS and DS (follow-up duration: 10-197 months) were analyzed. Results: The median age at onset of spasms was 7 (2-16) months. EEG showed hypsarrhythmia in 10 infants, and patterns of diffusely disorganised background with multifocal independent spike-wave activity in the remaining five. Brain MRI (n=8) revealed no abnormality in 3, microcephaly in 2, delayed myelination in one, and minimal volume changes in 2. PET scans (n=5) showed diffuse glucose hypometabolism in 3, focal hypo- or hypermetabolism in 1 and 2 patients, respectively, and increased or decreased basal-ganglia metabolism in one each. Spasms disappeared in 8 patients (53.3%; six off medication), with girls (5/7; 71%) responding slightly better than boys (3/8; 37.5%). Seven of the 8 responders had shown hypsarrhythmia. Cessation of spasms was achieved by ACTH alone (n=1) or in combination with vigabatrin or zonisamide (n=1, each), and monotherapy with zonisamide (n=2), topiramate (n=1), prednisone (n=1), and ketogenic diet (n=1). Two patients showed evolution into complex partial seizure or Lennox-Gastaut syndrome. One child had dystonic cerebral palsy associated with perinatal asphyxia. Conclusions: Spasms developed relatively later in patients with IS and DS, compared to cryptogenic IS patients, and showed modest response to treatment. Girls appear to have a better treatment response, with presence of hypsarrhythmia may signal a better treatment outcome.