Background: Extreme heat events (EHE) are of increasing public health concern. In urban areas, micro-urban heat islands (MUHI) raise the possibility of increased mortality risk. This study identified MUHI in the city of Barcelona, Spain, using Landsat 7 thermal infrared imagery and overlaid them onto at-home deaths between 2000-2003, identified from a mortality registry and geocoded using the Google API. Hot days were defined as days with mean minimum temperatures above the 90th percentile of historic temperatures. Data were analyzed using a case-only design, with a logistic regression model adjusted for spatial autocorrelation. Results: In the period 2000-2003, at-home deaths in MUHI were associated with 15% greater odds of dying on hot days than at-home deaths outside of MUHI. Conclusions: MUHI were a risk factor for at-home deaths during EHE in the study period (2000-2003) in the city of Barcelona. In urban areas facing similar conditions (limited use of air-conditioning, among others), residents of MUHI may be at increased mortality risk during extreme heat events.