Patients with insulin-dependent diabetes mellitus (IDDM) may develop autonomic neuropathy (AN) and cardiac complications. The association between AN and cardiac dysfunction was assessed in 34 IDDM patients (age 40 years, diabetes duration 21 years, 15 women) by echocardiography/Doppler and autonomic nerve function tests. The expiration/inspiration ratio (E/I) was used to assess parasympathetic damage, and the acceleration and brake indices for assessment of sympathetic impairment. AN was present in 21 patients. Patients with abnormal E/I (n = 11) had lower E/A ratios than patients without AN; early to atrial peak filling ratio (E/Amax) was median 1.1 (inter-quartile range 0.2) vs 1.4 (0.7), p = 0.022; early to atrial integral filling ratio (E/Aintegral) was 1.7 (0.3) vs 2.3 (1.2), p = 0.006. Patients with AN and normal E/I (sympathetic neuropathy, n = 10) and patients without AN had similar E/A ratios. E/Aintegral was also lower in patients with abnormal E/I compared with patients with AN and normal E/I; 1.7 (0.3) vs 2.2 (0.7), p = 0.008. Systolic function and cardiac dimensions were generally unaffected and similar in the three groups. In conclusion, diastolic dysfunction and parasympathetic neuropathy are related in IDDM patients.