AIM: To examine healthcare resource utilization patterns and costs accrued by carcinoid syndrome(CS) patients with and without diarrhea.METHODS: We conducted a retrospective cohort study using Market Scan~® data from 1/1/2002-12/31/2012. Newly diagnosed CS patients had 1 medical claim for CS(ICD-9-CM code 259.2) plus either ≥ 1 additional claim for CS or for carcinoid tumors(ICD-9-CM 209.x), and had no evidence of CS for 1 year prior to index CS diagnosis, in commercially-insured patients < 65 years old. Patients were required to have continuous enrollment one year prior and after index date(first claim with CS diagnosis in the ID period). We identified patients with evidence of non-infectious diarrhea(ICD-9-CM codes 564.5 and 787.91) within one year from the index date. Overall and CS-related healthcare resource utilization and costs were compared between patients with and without non-infectious diarrhea during the one year period after the index date. RESULTS: There were 2822 newly diagnosed CS patients; 534(18.9%) had evidence of non-infectious diarrhea. Compared to patients without non-infectious diarrhea, non-infectious diarrhea patients more commonly had at ≥ 1 CS-related hospitalization(13.7% vs 7.2%), ≥ 1 CS-related ED visit(11.0% vs 4.4%), and CS-related office visits in one year(6.9 vs 4.1; all P < 0.001). After adjusting for demographics, region, number of chronic conditions and the Charlson Comorbidity Index, the proportions of patients with any and with CS-related hospitalizations were 9.7% and 6.8% higher, respectively, among non-infectious diarrhea patients compared to those with without noninfectious diarrhea(P < 0.001). Unadjusted costs were significantly higher among non-infectious diarrhea patients vs those without non-infectious diarrhea. The non-infectious diarrhea group was also more costly, with adjusted mean annual costs of $81610, compared to $51719 in the group without non-infectious diarrhea(P < 0.001). CONCLUSION: Diarrhea is burdensome and costly in CS patients. Reduction of CS-related healthcare expenditures may be achievable through preventive treatment and appropriate management of diarrhea in CS. AIM: To examine healthcare resource utilization patterns and costs accrued by carcinoid syndrome (CS) patients with and without diarrhea. METHODS: We conducted a retrospective cohort study using Market Scan® data from 1/1/2002-12 / 31/2012. Newly diagnosed CS patients had a medical claim for CS (ICD-9-CM code 259.2) plus either ≥ 1 additional claim for CS or for carcinoid tumors (ICD-9-CM 209.x), and had no evidence of CS for 1 year prior to index CS diagnosis, in commercially-insured patients <65 years old. Patients were required to have continuous enrollment one year prior and after index date (first claim with CS diagnosis in the ID period). -infectious diarrhea (ICD-9-CM codes 564.5 and 787.91) within one year from the index date. Overall and CS-related healthcare resource utilization and costs were compared between patients with and without non-infectious diarrhea during the one year period after the index date. RESULTS: There were 2822 newl Compared to patients without non-infectious diarrhea, non-infectious diarrhea patients more often had at ≥ 1 CS-related hospitalization (13.7% vs 7.2%), ≥1 CS-related ED visit (11.0% vs 4.4%), and CS-related office visits in one year (6.9 vs 4.1; all P <0.001). After adjusting for demographics, region, number of chronic conditions and the Charlson Comorbidity Index, the proportions of patients with any and with CS-related hospitalizations were 9.7% and 6.8% higher, respectively, among non-infectious diarrhea patients compared to those with non noninfectious diarrhea (P <0.001). Unadjusted costs were significantly higher among non -infectious diarrhea patients vs those without non-infectious diarrhea. The non-infectious diarrhea group was also more costly, with adjusted mean annual costs of $ 81610, compared to $ 51719 in the group without non-infectious diarrhea. (CONCLUSION: Diarrhea is burde nsome and costly in CS patients. Reduction of CS-related healthcare expenditures may be achievable through preventive treatment and appropriate management of diarrhea in CS.