A study of external natural radiation, cosmic and terrestrial components, was carried out with in situ measurements using NaI scintillation counters while driving along the roads in Costa Rica for the period July 2003-July 2005. The geographical distribution of the terrestrial air-absorbed dose rates and the total effective dose rates (including cosmic) are represented on contour maps. Information on the population density of the country permitted the calculation of the per capita doses. The average effective dose for the total cosmic component was 46.88+/-18.06 nSvh(-1) and the average air-absorbed dose for the terrestrial component was 29.52+/-14.46 nGyh(-1). The average total effective dose rate (cosmic plus terrestrial components) was 0.60+/-0.18 mSv per year. The effective dose rate per capita was found to be 83.97 nSvh(-1) which gives an annual dose of 0.74 mSv. Assuming the world average for the internal radiation component, the natural radiation dose for Costa Rica will be 2.29 mSv annually.