Stable isotopes archived in calcium carbonate cave deposits such as stalagmites have been widely used to reconstruct past climates. However, various processes can influence the isotope signal recorded in speleothems, potentially obscuring climate signals. Stalagmite oxygen isotopes can record the δ18O values of regional precipitation and hence hydroclimate, but processes such as soil and karst water evaporation, mixing, and seasonally biased carbonate precipitation may complicate the target signal. Stalagmite carbon isotopes can record soil metabolism, which is also related to hydroclimate, but are also impacted by kinetic effects during degassing and calcite precipitation. Here we compare high-resolution oxygen and carbon isotopes in a small stalagmite (5 cm in height) with a modern top from Companheira cave in in southern Portugal. Oxygen isotope ratios of the stalagmite indicate that calcite precipitation is in equilibrium with cave drip water. Equilibrium between calcite and drip water allows for the assumption that the isotopic signature of the stalagmite accurately reflects the isotopic signature of local precipitation. To develop a time series that ranges from 2018 to 1820 the stalagmite was progressively milled every 25 µm from the top until a distance of 4 mm was reached. Three time periods of hydroclimate change in the Algarve region can be observed in the δ18O record. High δ18O values from 1780 to 1890 indicate regionally stable and dry conditions during this time interval. The region began to experience general wetter and more variable climatic conditions after 1890, represented by a decrease in δ18O values. These wetter climatic conditions ended in 1960 when precipitation amounts appear to have decreased gradually until the present. Precipitation data obtained from weather stations indicate that a higher average annual rainfall occurred throughout most of 20thcentury followed by a gradual drying. Carbon data obtained from the stalagmite suggest that carbon isotope fractionation is being driven by factors other than just soil metabolism. However, this study does support the idea that speleothem δ18O of calcite accurately reflects precipitation amounts. Further development of these time series will allow for a more comprehensive evaluation of dynamical changes in the regional climate system through time, particularly in the spatial extent and intensity of the Azores High, a system which strongly impacts precipitation in this region.