Passive solar architecture strategies such as adjusting building form and orientation, and using thermal insulation to improve users' comfort are commonly used. Nowadays, an increasing number of buildings are air-conditioned, and some passive techniques may not yield the anticipated energy reduction in these buildings. In addition, some strategies might seem contradictory such as decreasing the exposed surface area of building and that of setting large ones but thermally insulated.   This paper questions the effect of building form and orientation on the energy consumption of air-conditioned low-rise residential buildings in comparison to that of using thermal insulation in external walls for different desert environments. A base case of a squared two-storey residential building was simulated using the Energy-Plus software in three cities: Jeddah, Cairo and Alexandria. It was compared with other building forms: rectangles of different proportions, L, U, H-shaped forms and a squared courtyard building.   Results showed that common desert building forms do not always yield the expected reduction of energy consumption. The un-insulated courtyard building consumed 15% more energy in comparison with the square shaped building in the extreme hot climate of Jeddah, but when insulated, its performance improved to achieve savings of 17%, which was more than the savings achieved by the insulated solid square.  This trend was evident to a less extent in Alexandria; the courtyard reached 5% increase of energy consumption, while the insulated one reached 19% savings, to be one of the highest efficiency forms.   The effect of orientation varied according to the proportions of the forms, and thus, to the increase or decrease of the portion of surface area subjected to direct solar radiation. In general, thermal insulation proved to be of a higher effect than building form and orientation in almost all cases.