OBJECTIVE To delineate the difference in sundowning of wandering behavior between patient with Alzheimer Disease (AD) and frontotemporal dementia (FTD). METHODS The study was conducted in a dementia care unit at A hospital in Osaka, Japan from September 2008 to September 2009. Twenty-four-hour movements of 27 ambulatory inpatients with AD and 7 with FTD were coded consecutively by the IC tag monitoring system. RESULTS Repeated measures ANOVA after the adjustment of Huynh-Feldt Epsilon (H-F) showed no significant difference in 24 h standardized activity level between two groups (F = 3.74, P = 0.06), and there was no interaction between diagnosis and time (F = 1.42, P > 0.05). The standardized activity levels gradually increased from late afternoon to evening and then reached the highest point at 18:00 in AD group and 19:00 in FTD group. Test of within-subjects contrasts for order 17 was significant (F = 5.24, P < 0.05) and for order 9 was a tendency of significant (F = 4.26; P = 0.05) between two groups. AD group was significant greater active at 5:00, 6:00 and 7:00 (0.75 ± 0.08 vs 0.35 ± 0.16, F = 4.91; 1.13 ± 0.13 vs 0.49 ± 0.26, F = 5.06; 1.24 ± 0.15 vs 0.56 ± 0.28, F = 4.47 respectively, P < 0.05), and less active at 16:00 (1.65 ± 0.11 vs 2.22 ± 0.22, P < 0.05) comparing to FTD group by Bonferroni's multiple comparison test. Meanwhile, the time of peak value of hourly distance moved per day (PV-time) was delayed in FTD group comparing to AD by circular χ² test (14:12 ± 5:12 vs 15:47 ± 4:19, χ² = 87.31, P < 0.01). CONCLUSIONS The study suggests great possibility of sundowning of wandering behavior in both two subtypes with different temporal pattern of wandering behavior. Comparing to FTD patients, AD patients showed an advanced PV-time and prolonged active phase.