Pulmonary alveolar proteinosis (PAP) is a rare disorder in which lipoproteinaceous material accumulates in alveoli. A 47-year-old white man with a 15–pack-year smoking history visited his primary care physician for progressive shortness of breath. A chest radiograph showed diffuse pulmonary opacification. A high-resolution chest computed tomographic scan showed the crazy-paving pattern of diffuse interstitial and ground-glass opacification throughout the lung fields (Figure 1). A wedge lung biopsy was performed; histologic examination showed periodic acid–Schiff (PAS)–positive granular material (Supplemental Figure, available online at http://www.mayoclinicproceedings.org ) and alveolar macrophages with intracytoplasmic debris consistent with PAP.