Shape effects of drug delivery vehicles are largely unexplored, especially in vivo, but flexible cylinders have recently been shown to circulate in mice and rats longer than spheres of the same composition. Degradable worm-like filomicelles are shown here to have significant advantages for drug delivery in vivo. Not only is drug loading of the hydrophobic drug paclitaxel (tax) substantially increased with a cylindrical geometry compared to sonication-generated spherical micelles of the same copolymer, but intravenous injection of tax-loaded filomicelles nearly doubles the maximum tolerated dose in mice. In tumor-bearing mice, the higher dose of tax produced greater and more sustained tumor shrinkage. Apoptosis with filomicelles was also more pronounced in the tumor than in non-tumor organs, and drug biodistribution confirmed the enhanced tumor-selectivity of delivery. Flexible worm-like filomicelles thus increase both dosage and tumor-selective effects in vivo relative to spherical micelles and thus appear promising as anticancer drug delivery systems.