OBJECTIVE: Direct measurement of collagen glycation requires skin biopsy, which is invasive. We hypothesized that measurement of plantar fascia thickness (PFT) by ultrasound is an alternative index of tissue glycation and a marker of microvascular disease. RESEARCH DESIGN AND METHODS: This was a prospective longitudinal study of microvascular complications in 344 adolescents with type 1 diabetes, whose PFT was assessed by ultrasound at baseline. Retinopathy was assessed by seven-field fundal photography, albumin excretion rate (AER) measured from three consecutive timed overnight urine specimens, autonomic neuropathy by pupillometry and cardiovascular tests, and peripheral neuropathy by vibration and thermal thresholds. Longitudinal analysis was performed using generalized estimating equations with baseline PFT, duration, and A1C as explanatory variables. RESULTS: At first assessment, median (interquartile range) age was 15.1 (13.5-17.2) years and diabetes duration was 8.5 (6.0-11.5) years. Median follow up was 3.2 (2.1-4.5) years with a median of 4 (2-13) complications assessments per patient. In multivariate analysis, baseline PFT (abnormal in 132 subjects, 38%) predicted subsequent development of retinopathy (odds ratio 2.4 [95% CI 1.1-5.0]), elevated AER (2.24 [1.05-5.11]), peripheral neuropathy (2.3 [1.2-4.41]), and autonomic neuropathy (4.94 [2.46-9.91]). Limited joint mobility was present in only 4%. CONCLUSIONS: PFT is a significant predictor of the subsequent development of complications in type 1 diabetes, suggesting that glycation and oxidation of collagen in soft tissues may be independent risk factors for microvascular complications.