From The Vault
Small Frame is a Trait which appears in Fallout, Fallout 2, Fallout Tactics, Van Buren, Lionheart and J.E. Sawyer's Fallout RPG.
Fallout, Fallout 2
You are not quite as big as other people, but that never slowed you down. You can't carry as much, but you are more agile. You get a +1 bonus to your Agility, but your carry weight is equal to 25 + (15 lbs. x your Strength).
Fallout Tactics, Lionheart
You are not quite as big as other people, but that never slowed you down. You can't carry as much, but you are more agile. You get a +1 bonus to your Agility, but your carry weight is 50 pounds less than normal. Feralkins may not take this trait.
J.E. Sawyer's Fallout RPG
You are smaller than average. It's hard for you to carry heavy loads, but it's easy to avoid the lumbering giants of the wasteland. -50 to Carry Weight, +2 to Evade.
When combined with Power Armor, Small Frame can have some odd effects. Your intrinsic carry weight will be calculated using the 15lb/point stat, while the "bonus" carry weight from the armor's strength boost will be calculated with the standard 25lb/point. This means that if you take the opportunity to improve your intrinsic strength (for example, because you feel that having a few extra hitpoints is essential - despite the fact that by the time you can do this, you're effectively unkillable anyway), your carry weight will decrease by 10lb.
When selecting this perk during character creation, the +1 agility can be subtracted and put into any other category. This makes Small Frame a useful bonus to any statistic.