Introduction: Developmental and epileptic encephalopathies (DEE) are a heterogeneous group of severe neurodevelopmental disorders characterised by early-onset refractory seizures and developmental impairment. Advances in genomic sequencing have improved diagnostic yield, enabling precise molecular classification and guiding management. This case series describes the clinical and genetic spectrum of DEE identified through whole exome sequencing (WES) in a paediatric cohort from Sri Lanka. Case presentation: We present a case series of eight children (6 females, 2 males) withsuspected DEE or closely related neurodevelopmental epileptic disorders evaluated using WES. Age at presentation ranged from 3 months to 11 years. Core clinical features included earlyonset refractory epilepsy , global developmental delay or regression, hypotonia, infantilespasms, encephalopathic EEG patterns, and variable dysmorphism. Neuroimaging ranged from normal to diffuse cerebral or white matter abnormalities. Pathogenic or likely pathogenic variants were identified in DEE-associated genes, including KCNQ2, SCN8A, SPTAN1, IQSEC2, DNM1, ATP6V1A, EEF1A2, and ATP1A3. Variant types included de novo and inherited missense variants, nonsense variants, frameshift variants, and canonical splice-site variants, predominantlyaffecting autosomal dominant genes, with occasional autosomal recessive inheritance. Several cases demonstrated overlapping syndromic or metabolic features, underscoring phenotypic complexity . Conclusions: This series highlights the broad phenotypic and genetic spectrum of DEE, theutility of WES in achieving molecular diagnoses, and the importance of precise genotype–phenotype correlation. Early genetic diagnosis informs prognosis, treatment strategies, and family counselling, emph asising the need for genomic testing in children with unexplained epileptic encephalopathy .