A suicide bomber driving a minibus blew himself up outside a cafe in a mainly Shia Muslim district of the Iraqi capital, killing at least 38 people.
At least 12 people were killed in a spate of suicide bomb attacks on security personnel and government buildings earlier in the day, police said.
Violence in Iraq, which had eased after reaching a climax in 2006 -07, is now rising again.
More than 7,000 civilians have been killed this year, according to monitoring group Iraq Body Count.
There was no immediate claim of responsibility for any of the attacks, but Shias are viewed as apostates by Sunni Islamist militants whose insurgency has revived this year.
The explosion this evening took place in Baghdad's Amil neighbourhood.
"The cafe was full of people watching a soccer game andothers smoking shisha (water pipe) when a minibus drove over the pavement and exploded right at the entrance to the cafe," said Ali Mahdi, a policeman whose patrol was stationed nearby.
He said: "At first people in the cafe thought it was a drunk driver, until the blast tore them apart, covering the ground with chunks of human flesh and severed limbs."
Sectarian tensions in Iraq and the wider Middle East have been exacerbated by the Syrian civil war.
The Syrian civil war has drawn Sunnis and Shias from across the region and beyond into battle.
Al-Qaeda's Iraqi affiliate was forced underground in 2007 but has been invigorated by the war in Syria.
There is also growing Sunni resentment of Iraq's Shia-led government, which came to power after the US-led invasion in 2003.
Sunnis feel their minority sect has lost out since the overthrow of Saddam Hussein, and many took to the streets in protest late last year.