Primary colon carcinoma within an inguinal hernia sac is very rare and most reported cases were found at emergency open surgery for an incarcerated hernia. We report a case of incarcerated sigmoid colon carcinoma diagnosed preoperatively and treated with elective laparoscopic surgery. A 67-year-old man with a 2-year history of swelling of the scrotum and a breast lump was referred to us for surgical treatment of an irreducible left inguinal hernia and a right breast tumor. Blood examination results showed severe anemia. Computed tomography scan and endoscopic biopsy confirmed sigmoid colon carcinoma incarcerated in the left inguinal hernia. Thus, we performed definitive laparoscopic sigmoidectomy and conventional hernia repair for preoperatively diagnosed sigmoid colon carcinoma within an inguinal hernia.