Aim: To investigate the prevalence and clinical correlates of overprescribing and underprescribing of low molecular weight heparins (LMWHs) for thromboprophylaxis among older medical inpatients. Methods: Eight hundred seventy six patients (mean age 81.5 ± 7.6 years, female gender 57.2 %) enrolled in a multicenter observational study of seven acute care wards of geriatric medicine in Italy. The risk of venous thromboembolism was ascertained by calculating the Padua score for each patient. Patients receiving appropriate prescription of LMHW during stay were compared to those receiving LMHW with a Padua score <4 (overprescribing group). Similarly, patients with a high thromboembolic risk (Padua score ≥4) but not receiving LMHW (underprescribing group) were compared to patients appropriately not receiving LMHW during stay. Independent correlates of overprescribing and underprescribing were investigated by logistic regression analysis. Results: Overall, 42.8 % of patients had a Padua score ≥4. LMWHs were overprescribed in 7.3 % and underprescribed in 25.2 % of patients. The number of lost basic activities of daily living (BADL) (OR = 0.25; 95 % CI 0.15–0.41) and the number of diagnoses (OR = 0.76; 95 % CI 0.61–0.95) were inversely associated with LMWH overprescription. Conversely, older age (75–84 years: OR = 2.39; 95 % CI 1.10–5.19—85 years or more: OR = 3.25, 95 % CI 1.40–7.61), anemia (OR = 1.80, 95 % CI 1.05–3.16), pressure sores (OR = 4.15, 95 % CI 1.20–14.3), number of lost BADL at the admission (OR = 3.92, 95 % CI 2.86–5.37) and number of diagnoses (OR = 1.29, 95 % CI 1.15–1.44) qualified as significant correlates of LMWH underprescription. Discussion: Underprescription and, to a lesser extent, overprescription still represent an issue among older medical inpatients. Conclusion: Implementing risk-stratifying scores into clinical practice may improve appropriateness of LMWHs prescribing during hospitalization