Prior data in women suggest that incident clinically undiagnosed radiographic vertebral fractures (VFs) often are symptomatic, but misclassification of incident clinical VF may have biased these estimates. There are no comparable data in men. To evaluate the association of incident clinically undiagnosed radiographic VF with back pain symptoms and associated activity limitations, we used data from the Osteoporotic Fractures in Men (MrOS) Study, a prospective cohort study of community-dwelling men aged >/=65 years. A total of 4396 men completed spine X-rays and symptom questionnaires at baseline and visit 2, about 4.6 years later. Incident clinical VFs during this interval were defined by self-reported clinical diagnosis plus community imaging showing a centrally adjudicated >/=1 increase in semiquantitative (SQ) grade in any thoracic or lumbar vertebra versus baseline study X-rays. Incident radiographic VFs (>/=1 increase in SQ grade between baseline and visit 2 study X-rays) were categorized as radiographic-only (not clinically diagnosed) or radiographic plus clinical (also clinically diagnosed). Multivariable-adjusted log binomial regression was used to calculate prevalence ratios (PRs) and 95% confidence intervals (CIs). Men with incident radiographic plus clinical VF were most likely to have back pain symptoms and associated activity limitation at follow-up. However, versus men without incident VF, those with incident radiographic-only VF also were significantly more likely at follow-up to report any back pain (70% versus 59%; PR, 1.2 [95% CI, 1.1 to 1.3]), severe back pain (8% versus 4%; PR, 1.9 [95% CI, 1.1 to 3.3]), bother from back pain most/all the time (22% versus 13%; PR, 1.7 [95% CI, 1.3 to 2.2]), and limited usual activity from back pain (34% versus 18%; PR, 1.9 [95% CI, 1.5 to 2.4]). Clinically undiagnosed, incident radiographic VFs were associated with an increased likelihood of back pain symptoms and associated activity limitation. Results suggest incident radiographic-only VFs often were symptomatic, and were associated with both new and worsening back pain. Preventing these fractures may reduce back pain and related disability in older men.