Daily precipitation in the Swiss valleys decreases frequently with altitude, particularly in southern Switzerland. Only one-third of precipitation days show positive precipitation gradients with a fairly strong correlation of precipitation with altitude (R2 > or = 0.5). Generally, precipitation gradients are larger in the north than in the south but there are large differences among valleys situated near to each other. The effects of precipitation amount, weather situation, region and season, wind speed and topography were not very significant at all. It seems that the positioning of the upper and lower precipitation gauges under specific topographic and climate conditions can affect the precipitation gradients in a particular valley.