['Goblet cell carcinoid (GCC) and appendiceal mucinous neoplasms (AMNs) are considered as different appendiceal tumors. Coexistence of both tumors was occasionally noted. We further observed the concurrence in both primary tumors and their peritoneal dissemination, that is, peritoneal carcinomatosis (PC) including pseudomyxoma peritonei (PMP).', 'Review of our 10-year file identified two subgroups of cases with such concurrence. Group 1 is 14 cases of PC/PMP treated by surgical cytoreduction. Morphologic components of GCC, low-grade mucinous neoplasm (LMN), mucinous adenocarcinoma (MCA), and non-mucinous adenocarcinoma (NMCA) were identified separately in different organs/tissues. Group 2 is eight cases of localized primary tumors of appendix and ileocecal junction.', 'In Group 1, primary tumors (11 GCC, 1 GCC\u2009+\u2009LMN, 1 MCA, 1 NMCA) were identified in appendix (13) and in rectum (1). Further review identified mixed morphologic components in 7/12 GCC cases, including GCC\u2009+\u2009LMN (2), GCC\u2009+\u2009MCA (2), GCC\u2009+\u2009NMCA (1), and GCC\u2009+\u2009MCA\u2009+\u2009NMCA (2). Over peritoneal dissemination, GCC and/or other components were coexistent at different sites and in variable combinations. In Group 2, primary tumors were initially diagnosed as GCC (7) and MCA (1). Further review identified mixed components in all cases, including GCC\u2009+\u2009LMN (3), GCC\u2009+\u2009LMN\u2009+\u2009MCA (3), GCC\u2009+\u2009MCA\u2009+\u2009NMCA (2).'] Are appendiceal goblet cell carcinoid and mucinous neoplasms closely associated tumors : lessons from their coexistence in primary tumors and concurrence in peritoneal dissemination?