Elucidation of the pathways for intracellular transport of cholesterol is an important yet elusive goal in cell biology. Analysis of the cellular defects in the human disease Niemann-Pick C (NP-C) is providing insights into this problem. Cholesterol derived from low-density lipoprotein accumulates in lysosomes of NP-C cells, apparently because intracellular movement of such cholesterol is blocked. Identification of the NP-C gene should provide crucial molecular clues to the mechanism of cholesterol transport within cells.