Three studies were conducted to evaluate the validity and reliability of the three measures of the Communication and Symbolic Behavior Scales Developmental Profile (CSBS DP): (1) a one-page parent-report checklist; (2) a four-page follow-up caregiver questionnaire (CQ); and (3) a behavior sample (BS), which is a face-to-face evaluation of the child. Participants for these studies were drawn from a pool of 603 children for the checklist and CQ (ages 6-24 months) and 364 children for the BS (ages 12-24 months). Study 1 examined the concurrent relationship of standard scores for the checklist, CQ, and BS. Large correlations were found between the checklist and CQ and moderate to large correlations were found between each of the parent report tools and the BS. Study 2 examined test-retest stability by comparing the raw and standard scores over a 4-month retest interval. The results indicated significantly greater retest raw scores but no significant differences between standard scores from test to retest for the checklist, CQ and BS, providing evidence that the three measures detect growth over short periods but produce relatively stable rankings of children. Study 3 examined the concurrent and predictive relationship of the three CSBS DP measures and children's outcomes on standardized tests of receptive and expressive language at 2 years of age. Moderate to large correlations were found between all of the CSBS DP measures and language outcomes at 2 years of age. Multiple regression analyses indicated that the three composites were a significant predictor of receptive and expressive language outcomes. The findings from these three studies support the use of the CSBS DP as a screening and evaluation tool for identifying children with developmental delays at 12 to 24 months of age.