In early December, Nicolò Villa, a jeweler from Milan, was in Manhattan for a trunk show when he spotted a pre-owned Rolex Lady-Datejust with a blue-green opal dial in a shop on West 47th Street. At 26 millimeters in diameter, the watch’s two-tone case was only slightly larger than a 25-cent piece.

Mr. Villa bought the relatively diminutive watch for his mother but had a change of heart before giving it to her.

“I felt comfortable wearing it,” Mr. Villa said at a gem show in Tucson, Ariz., in February, as he gazed down at the Lady-Datejust, now at home on his right wrist.

“I’m liking more the very flat styles, and I’m going smaller,” he explained. “It feels more elegant. I’m not such a big guy. Proportions for me are very important.”

Mr. Villa’s style choice is hardly news to watch lovers, who have spent the past year obsessing over the vogue for shrinking cases. While size preferences have ballooned over the years — veterans of the watch world may recall that in the early 2000s, Brobdingnagian-size watches, some as big as 50 millimeters, reigned supreme — the aesthetic trend du jour is undeniably dainty and surprisingly feminine.

And even though many of the timepieces debuting this week at the Watches and Wonders fair in Geneva won’t reflect the downsizing trend (owing to the watch industry’s lengthy production cycles), the talk of the town is bound to be the relatively sudden, social media-fueled ubiquity of smaller case sizes.