BACKGROUND Behavioral research to improve lifestyle in broadly defined populations of patients with type 2 diabetes is limited. OBJECTIVE We evaluated a behavioral intervention featuring technology-based self-monitoring on biophysiologic outcomes of glycemic control and markers of cardiovascular risk. DESIGN In this single-site, randomized clinical trial, participants were stratified by good and poor glycemic control (glycated hemoglobin <8% or ≥8%) and absence or presence of kidney disease, (estimated glomerular filtration rate ≥60 or <60 mL/min) and randomized within strata. Measurements were obtained at 0, 3, and 6 months. PARTICIPANTS/SETTING Self-referred, community-dwelling adults with type 2 diabetes mellitus. INTERVENTION The intervention group received Social Cognitive Theory-based counseling paired with technology-based self-monitoring, and results were compared with an attention control group. MAIN OUTCOME MEASURES Glycated hemoglobin, fasting serum glucose, lipid levels, blood pressure, weight, body mass index, and waist circumference were evaluated. STATISTICAL ANALYSES PERFORMED Mean differences within and between randomization groups were compared over time. Intervention effects over time were estimated using random intercept models. RESULTS Two hundred ninety-six subjects were randomized, 256 (86.5%) completed 3-month and 246 (83.1%) completed 6-month assessments. Glycated hemoglobin was reduced in the intervention group by 0.5% at 3 months and 0.6% at 6 months (P<0.001 for each), and the control group by 0.3% (P<0.001) at 3 months and 0.2% (P<0.05) at 6 months; but between-group differences were not significant. In those with baseline glycated hemoglobin ≥8% and estimated glomerular filtration rate ≥60 mL/min, glycated hemoglobin was reduced in the intervention group by 1.5% at 3 months and 1.8% at 6 months (P<0.001 for each), and the control group by 0.9% (P<0.001) at 3 months and 0.8% (P<0.05) at 6 months; but between-group differences were not significant. In random intercept models, the estimated reduction in glycated hemoglobin of 0.29% was not significant. CONCLUSIONS Two behavioral approaches to improving general lifestyle management in individuals with type 2 diabetes mellitus were effective in improving glycemic control, but no significant between-group differences were observed.