The 1991 Survey of Recent College Graduates (RCG:91) is the sixth study in a series begun in 1976. The series provides data on the occupational and educational outcomes of recent bachelor's and master's graduates one year after graduation. The survey was conducted by Westat, Inc. in a two-stage sample involving 400 institutions of higher education and 18,000 graduates contacted by telephone. Along with estimates, reports on the RCG typically include standard errors of the estimates, indicating the nature and size of sampling error. Errors due to nonsampling error are often not included in estimated standard errors, but this report examines nonsampling errors and their impact on the estimates from the RCG:91. The major sources of nonsampling errors are nonresponse, random measurement errors, and systematic errors due to interviewers. Each source is discussed, and ways to estimate the potential consequences of nonsampling errors are explored. Nine figures, 19 tables, and 3 exhibits present statistical information. Eight appendixes contain supplemental and detailed information about the conduct of the survey. (SLD)