Low back pain (LBP) is a high-burden condition that lacks routine surveillance data. Health administrative data may be used for surveillance, but their validity for measuring LBP in the general population has not been established. We aimed to (1) determine the validity of health administrative data to measure LBP compared to self-reported LBP in a population-based sample of Ontario adults; and (2) describe the differences in characteristics of LBP cases based on data sources. Adult respondents (≥18 years) of the Canadian Community Health Survey (CCHS) from 2003 to 2012 were included (N = 150,695). Canadian Community Health Survey data were individually linked to health administrative data, including Ontario Health Insurance Plan and hospitalization data. The reference standard was defined as self-reported back problem diagnosed by a health professional in the CCHS. Measurement of LBP from billing records was defined as ≥1 physician billing or procedural code for LBP during the year preceding CCHS interview date. We measured concurrent validity by comparing prevalence, agreement (kappa), and accuracy (sensitivity, specificity, and positive and negative predictive values [PV]) of administrative data to measure LBP. Prevalence of LBP was higher using self-reported (21.2%) than administrative data (10.2%), and agreement was low (kappa = 0.21). Administrative data had sensitivity 23.9% (95% CI 23.1-24.6), specificity 93.4% (95% CI 93.2-93.7), positive PV 50.4% (95% CI 49.1-51.7), and negative PV 82.0% (95% CI 81.7-82.3). Characteristics of LBP cases based on data sources differed in sex, health/behaviour characteristics, and allied health care utilization. Using health administrative data significantly underestimates the prevalence of LBP. This can lead to misclassification bias that is likely nondifferential in epidemiological studies.