The goals of this study are to determine the frequency of anticardiolipin antibodies (ACA) in patients with various diseases and to evaluate the clinical significance of ACA in Taiwan. We collected 690 patients from ACA laboratory records. They were divided into eight groups in order to compare ACA percentages. Positive rates of ACA in different disease groups were below 20%, except for 38.2% in autoimmune diseases with vascular thrombosis. Compared with old stroke, the ACA positivity in young stroke was not significantly different (P = 0.482). The positive percentage of lupus anticoagulant (LA) (2.86%) was lower than that of ACA (15.66%) in young stroke (P = 0.015). Among patients with pregnancy loss or prematurity, the ACA positivity in lupus patients (44.44%) was higher than without lupus (9.76%; P = 0.01). The prevalence of ACA is higher in patients with vascular thrombosis complicated by autoimmune diseases than with thrombosis alone in Taiwan. Young and old stroke do not differ in ACA positivity. Moreover, ACA is more prevalent than LA for young stroke related coagulation. The ACA positivity for pregnancy loss or prematurity is very low in Taiwan. In summary, this is the first report on the frequency of ACA and other coagulation factors in various diseases in Taiwan.