Low concentration of mannan-binding lectin (MBL) has been related to unexplained spontaneous abortion (SA), which has also been observed in an increased frequency in patients with celiac disease (CD). In this study, plasma levels of MBL were determined in patients with CD and irritable bowel syndrome (IBS) in order to investigate whether there is an association of MBL levels and the occurrence of SA in these patients. MBL concentration was determined in 46 patients with CD (28 without and 18 with report of SA) and 38 patients with IBS (25 without and 13 with report of SA). A higher frequency of SA was observed in women with CD when compared to IBS patients (23.2 vs. 13.9%; P = 0.046). No significant difference was observed in MBL concentrations between patients with CD, IBS, and healthy controls, nor between patients with or without occurrence of SA. These results suggest that the serum levels of MBL and the occurrence of SA in women with CD and IBS are not causally related.