Background: Studies have shown that familial type 1 diabetes patients (FTID) have less severe metabolic derangement at presentation compared to sporadic patients (ST1D), but data on long-term metabolic control are lacking. Objective/Hypothesis: (1) FT1D will have less severe presentation and better HbA 1c over 5 years compared to ST1D; (2) HbA 1c in the offspring will correlate with parent HbA 1c in parent-offspring group; and (3) HbA 1c of the second affected sibling (SP2) will correlate with the first affected sibling (SP1) in sib-pairs. Methods: Cohort of 33 parent-offspring and 19 sib-pairs; controls included 33 sporadic subjects matched by age, sex, ethnicity, puberty, and insulin regimen. Paired t-test and Pearson’s correlation were used for statistical analysis. Results: At diagnosis, mean age in FT1D vs. matched ST1D (7.7±4.9 vs. 7.6±4.5 years), mean HbA 1c (9.6% vs. 10.7%), HCO 3 (21 vs. 18 meq/L), glucose (428 vs. 463 mg/dL) and pH (7.35 vs. 7.36; p=ns) were not different. At 5 years, HbA 1c (8.9% vs. 8.8%; p=0.81), clinic visits (12 vs. 12.5, p=0.68) and emergency room visits (0.48 vs. 0.24, p=0.10) were not different. In affected siblings, only HCO 3 was different (SP1:18 vs. SP2: 24 meq/L; p<0.01). HbA 1c for SP2 correlated positively with SP1 (r=0.67, p<0.01). Offspring HbA 1c correlated positively with affected parents (9.3% vs. 8.6%, r=0.57, p=0.18) but was not significant. Conclusion: Metabolic control at diagnosis and at 5 years was similar in FT1D and ST1D. In sib-pairs, the second affected sibling had milder clinical presentation compared to the first affected sibling.