Judd Apatow has followed up his surprise hit, “The 40-Year-Old Virgin,” with another ingratiating romantic comedy that might have been called “The 23-Year-Old Accidental Dad.”

The real title, “Knocked Up,” is a punchier summary of this gender-divide film about the aftermath of a one-night stand between an ambitious, gorgeous blonde named Alison and Ben, a slovenly slacker. Like “The 40-Year-Old-Virgin,” it successfully mixes raunchy humor and juvenile antics with tender touches and adult conflicts.

Writer/director Apatow gives us ...