Pulmonary interstitial glycogenosis (PIG) is an enigmatic lung disorder of unknown etiology that presents with neonatal respiratory distress. Despite its dramatic clinical presentation, the diagnosis of PIG has a favorable prognosis with rare mortality in the absence of comorbid conditions. In this report, we describe changes in successive lung biopsies in a neonate who presented with respiratory failure and pulmonary hypertension. Diagnostic lung biopsy at 10 days of age exhibited classic histologic and ultrastructural findings of PIG with diffuse expansion of the alveolar interstitium by glycogenated mesenchymal cells. Subsequent to the patient's clinical improvement, a repeat biopsy at 49 days of age showed significant resolution of the disorder. Colocalization of vimentin-immunopositive cells with both phospho-histone H3 and cleaved caspase-3 demonstrated prominent attenuation of mesenchymal cell proliferation and apoptosis in the second biopsy. Although the self-limited nature of PIG has been described clinically, it has never been documented histologically. We present this case to illustrate the clinical and pathologic resolution of the disorder and speculate that the lesional mesenchymal cells may have transient proliferative capacity.