A twenty-two year old Brazilian woman gives birth to her second daughter and is surprised in the delivery room. Her baby girl’s head looks drastically different from her first daughter’s. What happened? she asks her obstetrician. She did not have any ultrasounds in her third trimester, so the diagnosis of microcephaly is a surprise. However, she does recall a few days at the end of her first trimester when she had a mild fever and a rash. She also recalls many mosquito bites throughout her pregnancy. Her doctor tells her that she was probably infected with the Zika virus. Can her doctor tell her that Zika caused the microcephaly? Have scientists proven a causative connection?