Considerations of sample size computations in the medical literature have gained increasing importance over the past decade and are now often mandatory for scientific grant proposals, protocols, and publications. However, many surgeons are ill-prepared to understand the parameters on which the appropriate sample size is based. The present article has several objectives: first, to review the need for sample size considerations; second, to explain the ingredients necessary for sample size computations in simple, nonmathematic language; third, to provide options for reducing the sample size if it seems impracticably large; and fourth, to help avoid some of the more common mistakes encountered when computing sample sizes.