The Craugastor rugulosus species series has been one of the most affected clades by the decline of amphibian populations in Mesoamerica. These stream-dwelling frogs are threatened at all altitudinal ranges throughout their distribution. Craugastor ranoides is categorized as Critically Endangered on the IUCN Red List due to the disappearance of populations in the highlands and lowlands of Costa Rica. Currently the species is only found on the Santa Elena Peninsula. Additional ecological and natural history studies are necessary to formulate conservation plans for this species, which should include captive breeding programs and continuous monitoring of wild populations. We conducted a study of density, habitat use, and morphometrics of C. ranoides in three streams on the Santa Elena Peninsula Guanacaste, Costa Rica, during two consecutive dry seasons. The density of adult frogs and the probabilities of detection were similar during both dry seasons but we found differences in both parameters between streams. Counts of juveniles and subadults differed between seasons and between streams. Stream sector (50-m length) occupancy was approximately 80% during both dry seasons. We found most frogs motionless on boulders, but juveniles also frequented leaf litter. Sexual dimorphism was found in snout-vent length, mass, and tympanum diameter in subadults and adults. This study establishes a baseline for further monitoring of wild populations. Additional research and monitoring are necessary to detect possible changes in abundance and potential decline of these populations, which might be the only ones remaining in Costa Rica.