Summary A review of the literature relating weather variables to eclampsia suggests that to date the conclusions drawn have been severely compromised by methodological defects in study design and data analysis. The present study was carried out in Cali, Colombia, a city with only one public maternity hospital. Data on 156 eclamptic women and 465 control women were linked by computer to data on rain, temperature and relative humidity on the day of admission and on that day plus the previous two. The data show that eclampsia is related to maximum temperature and relative humidity during the five-year interval studied. Eclampsia rates are twice as high on cool or humid days than on days with average temperatures or humidities. This relationship persists even when one controls for seasonal fluctuations in number of births or in the proportion of parturients who were primiparae, very young, or unmarried.