Combine sugar, cocoa, milk, and butter in a heavy saucepan. Cook over medium heat, stirring constantly, until mixture reaches a slow boil (mixture will bubble around sides). Cook 2 additional minutes, stirring constantly.
Remove from heat; add peanut butter, and stir until smooth. Stir in oats, pecans, and vanilla.
Drop mixture by tablespoonfuls onto waxed paper. Cool.
Recipe submitted by Joyce on 5/15/00