In West Africa predictions of future changes in climate and especially rainfall are highly uncertain, and upto now no long-term analyses are available of the effects of climate on crop production. This study analyseslong-term trends in climate variability at N'Tarla and Sikasso in southern Mali using a weather datasetfrom 1965 to 2005. Climatic variables and crop productivity were analysed using data from an experimentconducted from 1965 to 1993 at N'Tarla and from a crop yield database from ten cotton growing districtsof southern Mali. Minimum daily air temperature increased on average by 0.05?C per year during theperiod from 1965 to 2005 while maximum daily air temperature remained constant. Seasonal rainfallshowed large inter-annual variability with no significant change over the 1965-2005 period. However,the total number of dry days within the growing season increased significantly at N'Tarla, indicating achange in rainfall distribution. Yields of cotton, sorghum and groundnut at the N'Tarla experiment varied(30%) without any clear trend over the years. There was a negative effect of maximum temperature,number of dry days and total seasonal rainfall on cotton yield. The variation in cotton yields was relatedto the rainfall distribution within the rainfall season, with dry spells and seasonal dry days being keydeterminants of crop yield. In the driest districts, maize yields were positively correlated with rainfall.Our study shows that cotton production in southern Mali is affected by climate change, in particularthrough changes in the rainfall distribution.