This paper describes an outdoor-indoor thermal investigation of a multifamily residential building during summer in Cairo, Egypt. Initially, microclimate meteorological data was generated for an urban settlement with and without trees being incorporated in to the development. The software ENVI-met was used for this first stage. Two kinds of tree planting (15m high Ficus Elastica and 20m Yellow Poinciana) were simulated, together with the existing scenario that has no trees. Next, the energy analysis package DesignBuilder used the modified microclimate data from ENVI-met to simulate indoor comfort levels in the residences. The Predicted Mean Vote (PMV) was used to quantify thermal comfort. The study found that the best indoor comfort levels were achieved using the 15m high Ficus Elastica trees in the urban site. The main conclusion from this investigation is that new urban developments in Cairo shouldn't only consider trees planting at the planning stage, but also a specific type should be used for better outdoor-indoor performance. Moreover, results indicate that raw weather data files used without microclimate physical adjustments are not adequate for detailed comfort analysis and indoor-outdoor simulations should be coupled for better representing indoor climate.