BACKGROUND Application of cardiac troponin T (cTnT) as a marker of myocyte damage requires knowledge of its measurement variability. Using a highly sensitive assay for measurement, we evaluated the long-term storage stability of plasma cTnT at −70 °C and the sources of cTnT variability. METHODS Samples from the Atherosclerosis Risk in Communities study collected in 1996–1998 and 2005–2006 were assayed centrally to quantify variability in cTnT attributable to processing (replicates from same blood draw, n = 87), laboratory (replicates after freeze thaw, n = 29), short-term (n = 40) and long-term biological variation (repeat visit, n = 38), and degradation in frozen storage (n = 7677). RESULTS Approximately 30% of this population-based cohort had cTnT concentrations below the detection limit (3 ng/L). Reliability coefficients for all paired comparisons exceeded 0.93 except for samples drawn 8 years apart (r = 0.36). Sources of cTnT variation (as CVs) were: laboratory, 2.1% and 11.2% in those with and without heart failure, respectively; processing, 18.3%; biological, 16.6% at 6 weeks and 48.4% at 8 years. The reference change value at 6 weeks (68.5%) indicated that 4 samples are needed to determine a homeostatic set point within ±25%. The estimated cTnT degradation rate over the first year in long-term frozen storage was 0.36 ng/L per year. CONCLUSIONS cTnT was detectable in approximately 70% of community-dwelling middle-aged study participants and stable in −70 °C storage. The variability in cTnT attributable to 1 freeze–thaw cycle is of small magnitude. The observed high laboratory and intraindividual (biological) reliability of cTnT support its use for population-based research, and in clinical settings that rely on classification and serial measurements.