Choline is an essential nutrient and can also be obtained by de novo synthesis via an oestrogen responsive pathway. Choline can be oxidised to the methyl donor betaine, with short-term supplementation reported to lower plasma total homocysteine (tHcy); however, the effects of longer-term choline supplementation are less clear. We investigated the effect of choline supplementation on plasma concentrations of free choline, betaine and tHcy and B-vitamin status in postmenopausal women, a group more susceptible to low choline status. We also assessed whether supplementation altered plasma lipid profiles. In this randomised, double-blinded, placebo-controlled study, forty-two healthy postmenopausal women received 1 g choline per d (as choline bitartrate), or an identical placebo supplement with their habitual diet. Fasting blood samples were collected at baseline, week 6 and week 12. Administration of choline increased median choline and betaine concentrations in plasma, with significant effects evident after 6 weeks of supplementation (P < 0·001) and remaining significant at 12 weeks (P < 0·001); no effect was observed on folate status or on plasma lipids. Choline supplementation induced a median (25th, 75th percentile) change in plasma tHcy concentration at week 6 of − 0·9 ( − 1·6, 0·2) μmol, a change which, when compared to that observed in the placebo group 0·6 ( − 0·4, 1·9) μmol, approached statistical significance (P = 0·058). Choline supplementation at a dose of 1 g/d significantly increases the circulating concentration of free choline, and can also significantly increase the concentration of the methyl donor, betaine, thereby potentially enhancing the betaine–homocysteine methyltransferase-mediated remethylation of tHcy. This trial was registered at http://www.controlled-trials.com/ISRCTN82708510.