The case of a Saudi man in his 90s who has married a girl of 15 has drawn widespread criticism on Twitter and other social media in the country.
Some Saudis have been asking whether the case amounts to trafficking or child abuse.
Local media reports say the man paid a dowry of $17,000 (£10,500) in order to get married to the girl.
A series of similar cases in recent years has drawn attention to the issue of child marriage in the kingdom.
The girl in the latest case was so frightened that on the wedding night she locked her husband outside the bedroom and eventually escaped back to her parents, local media reports say.
The husband is reported to be considering legal action to get either her or his dowry back.
The case reflects how online social networks have become a vital forum for public discussion in what has long been an opaque, even closed society, with Saudis now taking to Twitter faster than anywhere else in the world, the BBC's Middle East analyst Sebastian Usher reports.
Thousands of girls under 14 are reported to have been married off to richer, much older men, he adds.
There appears to be widespread support in Saudi society for a minimum age for marriage, which the authorities say they are working towards.
However, some of the most conservative religious scholars are still resisting the idea, while insisting that girls must have reached puberty before marriage.