Introduction: Incontinentia Pigmenti (IP) is a rare multisystem genodermatosis that segregates as an X-inherited dominant condition. Affected patients present skin manifestation, the earliest symptom, classified as 3 or 4 stages. Here we report on a case of a female infant with a clinically evident first phase of IP, caused by Δ4-10 deletion in the NEMO gene. It is documented that this is the first case of IP proven by genetic testing in Korea. Case : A baby girl was born by cesarean section due to breech presentation with a birth weight 2,790 g at 37+6 weeks\' gestation to a 31-year-old woman. At the time of birth, several vesicles, pustules and erythematous papules developed over the trunk, scalp, especially extremities and also alopecia on the vertex was showed. She was the second baby. His parents and her elder sister were healthy, and had no other comparable dermatobes. However, there were two spontaneous abortion on maternal obstetric history. On physical examination, there was no remarkable abnormality except the skin lesions. At the 2nd days of age, the size of vesicles and pustules were decreased and hyperpigmented macules and vesicles, crust formation were presented. However at the 7th days of age, multiple generalized erythematous scaly patch, papules, and grouped pustules with crusts on especially extremities were aggravated. Laboratory tests including blood chemistry analysis, urinalysis, VDRL, bacterial culture, Tzanck smear, KOH test, and TORCH serology were in the normal range or negative. However, eosinophilia and leukocytosis were reported by complete blood count. Radiologic findings in brain sonography, echocardiography, infantography were under normal limits. Ophthalmological findings and the EEG examination were within physiological limits. Histopathologically, hydrophic degeneration of basal layer, dyskeratotic cells throughout the epidermis, and predominant eosinophil infiltration were noted. A cytogenetic examination yielding normal female results (46, XX), was performed to exclude chromosomal aberrations. Multiplex and long PCR analysis revealed deletion of exon 4-10 in NEMO gene in the patient. Conclusion: On the basis of the vesicular skin lesion and histological examination as well as the results of PCR analysis, the diagnosis of incontinentia pigmenti was confirmed.