Background: Vitamin D, a potential cardiovascular risk biomarker, has an unclear role in the adverse left ventricle remodelling (LVAR) after acute myocardial infarction (AMI). Methods: To evaluate the impact of Vitamin D levels on LVAR in a prospective cohort study of patients with AMI. Results: 253 patients with AMI were studied, 81 of which (32%) developed, in median 4.1 months after AMI, LVAR. Age, sex, risk factors, type and location of the infarction, clinical presentation, timing and mode of revascularization did not differ between patients with and without LVAR. However, patients with LVAR had lower Vitamin D levels (12.6 vs. 18.7 ng/mL, p < 0.001), while higher Vitamin D at baseline protected against LVAR (for increase of 10 ng/mL HR 0.74, CI 0.61–0.90, p < 0.001). Plasma levels of C Reactive Protein (CRP), peak Troponin I, indexed left ventricular end systolic volume (LVESVI) and NYHA class at discharge predicted, in multivariate analysis, LVAR occurrence at follow-up. Moreover, the inclusion of Vitamin D improved the multivariate model, as shown by the area under the ROC curve (HR 0.82; CI 0.76–0.88, p < 0.001). During the follow-up of 25.5 (7–77) months, patients with LVAR had a worse event-free survival rate (HF, p = 0.012; combined event HF/mortality, p = 0.006), even when the analysis was restricted to patients with ST-elevation MI (p = 0.006). Conclusions: Low Vitamin D levels are associated with post-infarct LVAR.