Hardest hit was the province of Sind, where at least 36 people have died in the past two days. Several neighborhoods of the provincial capital Karachi have been flooded, and water and electricity supplies have been cut.
Another five people were reported to have died in the province of Belujistan.
The principal cause of death has been the collapse of roofs in the poorer neighborhoods, as well as electrocution from downed power lines.
Record rainfalls in Pakistan and India this year have resulted in significant loss of life and damage to infrastructure. According to official statistics, the total number of people killed as the result of heavy rains in South Asia in 2007 has exceeded 2,000 so far.