Southern Brazilian prehistoric coastal series were examined for the presence of spondylolysis. All defects occurred at the pars interarticularis, most at L5 (51%), with the vast majority bilateral and complete (86.2%). Frequencies decreased from young adulthood (54.2%) through mid-adulthood (33.3%) to older adulthood (12.5%), suggesting differential mortality among affected individuals. The high overall prevalence (29.6%) demonstrates that these groups experienced a strenuous lifestyle, with activities that required repetitive and vigorous movements of lumbar hyperextension and rotation. Archaeological data provide support to interpret this pattern. Throwing harpoons, rowing and wrestling fishing nets were likely the main activities associated with the defect among men. Continuous loading of weight, including plant resources, mollusks and nursing children, were probably the tasks associated with spondylolysis in women. Copyright © 2010 John Wiley & Sons, Ltd.