Functioning ovarian carcinoid tumors are well known to cause carcinoid syndrome. Recently, strumal and trabecular ovarian carcinoid tumors are reported to cause severe constipation possibly because of tumor-producing peptide YY (PYY). We studied a case of primary ovarian strumal carcinoid who had had severe constipation until the tumor was removed by surgical operation. Immunohistochemically, many tumor cells were strongly positive for PYY. By Northern blot and reverse transcription polymerase chain reaction analyses, PYY mRNA was expressed in a complete form as detected in normal human colon mucosa. From these findings, an ovarian strumal carcinoid is strongly suggested to express complete PYY mRNA and therefore complete PYY protein that results in severe constipation.