ABSTRACT: Assessments of sperm whale Physeter macrocephalus abundance based on invalid analyses of whaling data are common in the literature. Modern visual surveys have produced population estimates for a total of 24% of the sperm whale¹s globalhabitat. I corrected these assessments for whales missed on the track line and then used 3 methods to scale up to a global population. Scaling using habitat area, plots of 19th century catches and primary production produced consistent global populationestimates of about 360000 whales (CV = 0.36). This is approximately 20% of the numbers reproduced in current literature from invalid whaling-based estimates. A population model, based on that used by the International Whaling Commission¹s ScientificCommittee, and which considers uncertainty in population parameters and catch data, was used to estimate population trajectories. Results suggest that pre-whaling numbers were about 1110000 whales (95% CI 672000 to 1512000), and that the population wasabout 71% (95% CI 52 to 100%) of its original level in 1880 as open-boat whaling drew to a close and about 32% (95% CI 19 to 62%) of its original level in 1999, 10 yr after the end of large-scale hunting. Thus, widely held views about the status of spermwhale populations need considerable revision.