Background An important aspect of Alzheimer's disease (AD) is loss or impairment of cholinergic neurons. It is controversial whether there is a similar cholinergic impairment and cerebral deficit of acetylcholine (ACh) in the case of vascular dementia (VD). The purpose of this study was to explore the levels of ACh and choline (Ch) in the cerebrospinal fluid (CSF) of patients with AD and VD, and their possible relationship with cognitive impairment. Methods Twenty-two AD patients, twenty-two VD patients, and twenty normal controls were recruited and scored with a Mini-Mental State Examination (MMSE). CSF concentrations of ACh and Ch were measured using high-performance liquid chromatography with an electrochemical detector (HPLC-ECD) and the results were then compared to cognitive status. Results ACh concentrations in CSF of AD patients [(10.7 +/- 5.1) nmol/L] and VD patients [(16.8 +/- 7.4) nmol/L] were both significantly lower than in controls [(34.5 +/- 9.0) nmol/L, t = 10.67, P < 0.001; t = 6.91, P < 0.001]. Both results correlated positively with MMSE scores (r(s) = 0.88 and r(s) = 0.85, respectively, P < 0.01). The CSF concentration of Ch was significantly higher in VD patients [(887.4 +/- 187.4) nmol/L] compared to AD patients [(627.6 +/- 145.1) nmol/L, t = 6.4, P < 0.001] and controls [(716.0 +/- 159.4) nmol/L, t = 4.2, P = 0.002]. CSF Ch concentration showed no difference between AD patients and normal controls, nor did it correlate with MMSE score in any of the three groups. Conclusions The positive correlation between ACh deficit and cognitive impairment suggests that ACh is an important neurotransmitter for memory. The similar decrease in ACh concentration in AD and VD patients may imply a similar pathogenesis for the process of cognitive impairment involved in these two disorders. The elevated CSF levels of Ch in VD patients compared to AD patients may be useful diagnostically. Cholinesterase inhibitors may be helpful not only for AD patients, but also for VD patients.