BACKGROUND: Low-molecular-weight heparins (LMWHs) are used in the prevention and treatment of venous thromboembolism (VTE). Bleeding is the primary major complication of LMWH therapy, which is associated with dose. The administration of appropriate dosages of LMWHs depends on the patient's risk of VTE, risk of bleeding, bodyweight, and renal function. Therefore, LMWH prescribing is prone to errors. However, no earlier study has explored the frequency of prescribing errors with LMWH. PURPOSE: The aim of the study was to determine the frequency and determinants of in-hospital LMWH-prescribing errors. METHODS: A cross-sectional study was conducted to examine the frequency and determinants of LMWH prescribing errors between April and August 2014. We randomly selected 500 patients 18 years and older with at least one LMWH prescription during inpatient hospitalization. A prescribing error was a deviation from the internal hospital guidelines. Logistic regression estimated determinants of prescribing error. RESULTS: A prescribing error was present with 34% of all LMWH users. The most frequently recorded error was a dose that was not adjusted to body weight and/or renal function (85%). Prophylactic LMWH prescribing in medical wards was associated with a higher risk of prescribing error as compared with surgical wards. CONCLUSIONS: The frequency of prescribing errors was 34% in a tertiary care hospital. Being a patient with prophylactic LMWH use on a medical ward is a determinant for LMWH prescribing error. Interventions that will lead to better electronic recording of body weight and more awareness among medical doctors may reduce the total number of prescribing errors.