To study aspects of the microclimate in a shantytown (favela), in order to understand the influence of the land occupation pattern on its climatic parameters.The study was carried out in a shantytown located in the southwestern region of the city of São Paulo, Brazil, between February 19 and July 31, 2003, i.e. covering the whole autumn and parts of the summer and winter. The air temperatures were measured every hour on a microclimate scale, at four points within this densely populated shantytown and, as a control, on a tree-lined street nearby.In the summer, the average hourly temperatures in the shantytown were between 18.5 degrees C and 29.5 degrees C but, away from it, they were 2 degrees C to 3 degrees C lower at the hottest times of the day. In the autumn, the temperatures ranged from 15.5 degrees C to 25.5 degrees C and in the winter, 13.5 degrees C to 25.5 degrees C. The chilliest time in the shantytown was before dawn in the autumn and at 7 a.m. in the winter. The temperature variation was greater inside the shantytown than outside of it. The temperatures were within the comfort range for around 50% of the time. Temperatures below the lower limit (18 degrees C) were more frequent than those above the upper limit (24 degrees C). Temperatures above the upper limit were more frequent in the shantytown than outside of it.The land occupation is a temperature differentiation factor. In the shantytown, the temperatures were higher during the daytime (by up to 3 degrees C) and lower at nighttime (by 1 degrees C on average). The shantytown environment accentuated the temperature extremes, while the temperatures in the control street were milder.