From 1995 to 1999, we conducted an ecological study of thamin (Cervus eldi thamin) at Chatthin Wildlife Sanctuary in central Myanmar; we maintained records on deer sightings and radiotracked 11 adult male and 8 adult female deer. Based on 747 sightings, a 0.63:1.0 adult male : female ratio and 0.51:1.0 fawn : adult female ratio were observed. Mean group size was variable (1.0–5.9 deer) and showed seasonal differences, with few groups observed in August–September and groups of ≤70 individuals observed in March–April. Based on the fixed-kernel method, annual home range was 9.04 km² ± 5.67 SD and 7.25 km² ± 3.45 SD for males and females, respectively. Thamin increased their seasonal home range during the hot–dry season, possibly in response to decreased forage and water availability and increased mating activity. The observed synchrony of estrous onset (March–April) and fawning (October–November) in female thamin is unusual for a tropical cervid species, but reproductive seasonality appears timed to balance fawn survival with doe nutrition in a monsoon environment.