OBJECTIVE The main objective of this study was to determine the effect of gallbladder emptying acquisition time on gallbladder ejection fraction (GBEF) measurement obtained by fatty meal cholescintigraphy (CS). METHODS During fatty meal cholescintigraphy (CS), GBEF1 and GBEF2 were calculated 20 and 45 min, respectively, post meal ingestion on 50 healthy volunteers, 37 patients with chronic acalculous cholecystitis (CAC) and 20 non-CAC patients. GBEF1/GBEF2 was calculated and represented the percentage of GBEF occurred during 20 min after meal ingestion. The gallbladder was classified as ended pattern if it terminated contraction before the end of data acquisition or classified as continuous pattern if it continued to contract before the end of data acquisition. Mean GBEF in continuous pattern was compared with mean GBEF in ended pattern in each group. RESULTS Gallbladder emptying had two phases; early rapid phase and late slow phase. About two-thirds of ejected volume occurred within the rapid phase. About half of gallbladders in each group were classified as ended pattern while the other half was classified as continuous pattern. There was no significant difference in mean GBEF values between both patterns in each group. CONCLUSIONS GBEF measurement obtained by CS is not affected by further extension of gallbladder emptying data acquisition beyond the standard 45-60 min acquisition time.