The purpose of this study was (a) to describe traumatic experiences (TEs) prior to being adopted, (b) to identify groups of TEs in adoptees, and (c) to explore the relationships of a group membership with adoptees’ psychological disorders and adjustment. Data were drawn from 1616 participants in the Modern Adoptive Families Study, a nationwide survey of adoptive families that adopted a child via foster care adoption, private domestic adoption, or international adoption. Latent class analysis revealed four groups of TEs (moderate deprivation, high deprivation, multiple high adversity, and low adversity), based on TEs prior to adoption. The high deprivation group was associated with greater numbers of psychological disorders. The high deprivation group and the multiple high adversity group had lower psychological adjustment than the other two groups. The multiple high adversity group consisted of adoptees who were the oldest, adopted from foster homes, had more special health needs, and were not Asians. These findings explain heterogeneity of TEs in adoptees and suggest implications for post-adoption services that are sensitive to the characteristics of adoptees’ TEs, particularly for domestic adoptees.