Background We sought to assess the long-term evolution of left ventricular (LV) function using two-dimensional (2D) and three-dimensional (3D) speckle tracking echocardiography (STE) for the detection of preclinical diabetic cardiomyopathy, in asymptomatic type 1 diabetic patients, over a 6-year follow-up. Design and methods Sixty-six asymptomatic type 1 diabetic patients with no cardiovascular risk factors were compared to 26 matched healthy controls. Conventional, 2D and 3D-STE were performed at baseline. A subgroup of 14 patients underwent a 6-year follow-up evaluation. Results At baseline, diabetic patients had similar LV ejection fraction (60 vs 61%; P = NS), but impaired longitudinal function, as assessed by 2D-global longitudinal strain (GLS) (−18.9 ± 2 vs −20.5 ± 2; P = 0.0002) and 3D-GLS (−17.5 ± 2 vs −19 ± 2; P = 0.003). At follow-up, diabetic patients had worsened longitudinal function compared to baseline (2D-GLS: −18.4 ± 1 vs −19.2 ± 1; P = 0.03). Global circumferential (GCS) and radial (GRS) strains were unchanged at baseline and during follow-up. Metabolic status did not correlate with GLS, whereas GCS and GRS showed a good correlation, suggestive of a compensatory increase of circumferential and radial functions in advanced stages of the disease – long-term diabetes (GCS: −26 ± 3 vs −23.3 ± 3; P = 0.008) and in the presence of microvascular complications (GRS: 38.8 ± 9 vs 34.3 ± 8; P = 0.04). Conclusions Subclinical myocardial dysfunction can be detected by 2D and 3D-STE in type 1 diabetic patients, independently of any other cardiovascular risk factors. Diabetic cardiomyopathy progression was suggested by a mild decrease in longitudinal function at the follow-up, but did not extend to a clinical expression of the disease, as no death or over heart failure was reported.