The aim of this study is to determine the prevalence of herbal medicine usage among surgical patients in three hospitals in Trinidad. The study population comprised 303 surgical outpatients randomly selected from the three hospitals. All patients were over 18 years of age. Eligible participants either had surgery within the previous year or were due for surgery within the following 6 months. Of the 303 subjects, 121 (40%) reported the use of herbal medicines. Twenty-five percent of patients attending Hospital 1 used herbal medicines, compared with 41% at Hospital 2 and 55% at Hospital 3. The difference between the three hospitals was statistically significant (P=0.023). Allium sativum (garlic) was the most common herb used (74%), followed by Citrus sinensis (orange peel) tea (47%), Cymbopogon citratus (lemongrass) (39%), Aloe vera (aloe) (31%) and Panax ginseng (Asian ginseng) (26%). The prevalence of herbal medicine usage among interviewed patients in Trinidad is similar to the prevalence rate reported in the USA and Italy. The reported use of garlic was high, which is a concern as this herb may impact on bleeding in surgical patients. Herbal medicines may also influence heart rate, blood clotting and anaesthesia, which could put surgical patients at further risk. Due to the risk of potential complications, an accurate herbal medicine history should be obtained for all surgical patients.