Abstract: Indoor radon, at six communities located at altitudes between 2500 and 3000 m.a.s.l. in Central Mexico, has been measured in family houses and in offices and laboratories (handling no radioactive sources), from two close together buildings belonging to a nuclear facility. The radon measurements were performed with Honeywell A9000A devices. The indoor radon average value obtained in the family houses was 47 ± 23 Bq m-3, but, at least at one community indoor radon was found higher than action levels. At the two buildings from the nuclear facility, average indoor radon had one order magnitude difference between them. Short term peaks higher than action levels were eventually observed both at family houses and laboratories, particularly at rooms having not external windows. The average effective dose due to indoor radon for the general population was 1.19 m Sv y-1 and for workers, values reached up to 21 m Sv y-1. The additional dose due to working at a laboratory and living at a nearby community was estimated to be, in average, 5.16 m Sv y-1.