The relative importance of climate and humans in the disappearance of the Malagasy megafauna remains under debate. Data from southwestern Madagascar imply aridifcation contributed substantially to the late Holocene decline of the megafauna (the Aridifcation Hypothesis). Evidence for aridifcation includes carbon isotopes from tree rings, lacustrine charcoal concentrations and pollen assemblages, and changes in fossil vertebrate assemblages indicative of a local loss of pluvial conditions. In contrast, speleothem records from northwestern Madagascar suggest that megafaunal decline and habitat change resulted primarily from human activity including agropastoralism (the Subsistence Shift Hypothesis). Could there have been contrasting mechanisms of decline in different parts of Madagascar? Or are we lacking the precisely dated, high resolution records needed to fully understand the complex processes behind megafaunal decline? Reconciling these contrasting hypotheses requires additional climate records from southwestern Madagascar. We recovered a stalagmite (AF2) from Asafora Cave in the spiny thicket ecoregion, ~10 km from the southwest coast and just southeast of the Velondriake Marine Reserve. U-series and 14C dating of samples taken from the core of this stalagmite provide a highly precise chronology of the changes in hydroclimate and vegetation in this region over the past 3000 years. Speleothem stable oxygen and carbon isotope analyses provide insight into past rainfall variability and vegetation changes respectively. We compare these records with those for a stalagmite (AB2) from Anjohibe Cave in northwestern Madagascar. Lastly, odds ratio analyses of radiocarbon dates for extinct and extant subfossils allow us to describe and compare the temporal trajectories of megafaunal decline in the southwest and the northwest. Combined, these analyses allow us to test the Aridifcation Hypothesis for megafaunal extinction. The trajectories of megafaunal decline differed in northwestern and southwestern Madagascar. In the southwest, unlike the northwest, there is no evidence of decoupling of speleothem stable carbon and oxygen isotopes. Instead, habitat changes in the southwest were largely related to variation in hydroclimate (including a prolonged drought). The megafaunal collapse here occurred in tandem with the drought, and agropastoralism likely contributed to that demise only after the megafauna had already suffered drought-related population reduction. Our results offer some support for the Aridifcation Hypothesis, but with three caveats: frst, that there was no island-wide aridifcation; second, that aridifcation likely impacted megafaunal decline only in the driest parts of Madagascar; and third, that aridifcation was not the sole factor promoting Comparing the paleoclimates of northwestern and southwestern Madagascar during the late Holocene: Implications for the role of climate in megafaunal extinction Faina et al.: Comparing the paleoclimates of northwestern and southwestern Madagascar 109 megafaunal decline even in the dry southwest. A number of megafaunal species survived the prolonged drought of the first millennium, and then likely succumbed to the activities of agropastoralists.