Abstract Variation of radon concentration in ground water in the area of Northeastern Hungary was investigated. Specific geological features of this region result in high radon concentration in well waters (between 100 and 350 Bq l −1) and in the air of dwellings (occasionally as high as 10 000 Bq m −3). The observed radon concentrations of well waters show unpredictable variability both in space and time. In adjacent wells, concentration values may change by a factor of 10. In the case of some wells, a variation by a factor of 3–6 (between 20 and 180 Bq l −1) was measured during a year. Measurements were made in order to find correlations between radon concentration in soil air, radon concentration in water and meteorological parameters, i.e. external air pressure, temperature, wind speed and air humidity. A good correlation (with correlation coefficient of k=−0.84) between radon concentration in soil air and air pressure was found.