Spacing patterns of individuals within an island population of the Central American spiny rat Proechimys semispinosus were studied by radio-tracking eight adults for 2 months during the rainy season and eight adults for 1 month during the dry season in central Panama. All trees ≥10 cm diameter at breast height on the island were mapped, tagged, identified to species, and inventoried monthly to determine fruit production. Diurnal telemetry was conducted to locate daytime resting burrows. Burrow habitat was quantified by measuring nine variables at each burrow site. Individuals had larger home ranges and greater home-range overlap during the rainy season, and males had marginally larger home ranges than females. No evidence was found of attraction, avoidance or exclusive use of space by adult spiny rats. Thirty-six located burrows had nine instances of co-occupancy. Burrows were located close to water and had little herbaceous cover. The presence of broadly overlapping home ranges, larger home ranges of males vs females, greater numbers of burrows of females in home ranges of males vs those of females, and larger home ranges of sexually active males suggest that P. semispinosus had a promiscuous mating system within this population.