At least 38 people were killed in three bombings in Christian areas of Baghdad, including a car bomb that exploded as worshippers were leaving a Christmas service, Iraqi police and medics said.
Elsewhere in Iraq on Wednesday, at least 10 people were killed in three attacks that targeted police and Shia pilgrims, police said.
Iraq is enduring its deadliest violence in years, reviving memories of the sectarian bloodshed between Sunni and Shia Muslims that killed tens of thousands in 2006-07.
The day's deadliest incident occurred in the Doura district of southern Baghdad when the car bomb went off as Christians were emerging from a Christmas mass, killing at least 24 people.
Shortly before, two bombs in a crowded market in a separate, mostly Christian area of Doura killed another 10 people.
Ahmed Edan, a policeman on duty in the area of the attacks, said the sound of the first of the two explosions caused worshippers to leave the church.
"A car parked near the church exploded when the families were hugging each other goodbye before leaving. The blast was powerful," he said.
"Bodies of women, girls and men were lying on the ground covered in blood. Others were screaming and crying while they were trying to save some of their wounded relatives."
No one immediately claimed responsibility for the attacks in Baghdad, which also wounded 52 people.
The US embassy in Baghdad condemned the bombings, saying in a statement that Christians in Iraq had suffered "deliberate and senseless targeting by terrorists for many years, as have many other innocent Iraqis".
Iraq's fast-dwindling Christian minority has been a target of al-Qaeda Sunni fighters in the past, including a 2010 attack on a church that killed dozens of people.