OBJECTIVE: The objective of this study was to compare two diabetes self-management interventions designed for Mexican Americans: "extended" (24 h of education, 28 h of support groups) and "compressed" (16 h of education, 6 h of support groups). Both interventions were culturally competent regarding language, diet, social emphasis, family participation, and incorporating cultural beliefs. RESEARCH DESIGN AND METHODS: We recruited 216 persons between 35 and 70 years of age diagnosed with type 2 diabetes >/=1 year. Intervention groups of eight participants and eight support persons were randomly assigned to the compressed or extended conditions. The interventions differed in total number of contact hours over the year-long intervention period, with the major difference being the number of support group sessions held. The same information provided in the educational sessions of the extended intervention was compressed into fewer sessions, thus providing more information during each group meeting. RESULTS: The interventions were not statistically different in reducing HbA(1c); however, both were effective. A "dosage effect" of attendance was detected with the largest HbA(1c) reductions achieved by those who attended more of the extended intervention. For individuals who attended >/=50% of the intervention, baseline to 12-month HbA(1c) change was -0.6 percentage points for the compressed group and -1.7 percentage points for the extended group. CONCLUSIONS: Both culturally competent diabetes self-management education interventions were effective in promoting improved metabolic control and diabetes knowledge. A dosage effect was evident; attending more sessions resulted in greater improvements in metabolic control.