Presently, most mental health practitioners in the United States are educated, trained, and employed in a system focused on curing or changing autistic people. As a result, mental health practitioners may exhibit anti-autistic bias--any form of bias that degrades, devalues, or others autistic people or traits--when engaged with autistic clients. Since the collaborative relationship between therapist and client, termed the "therapeutic alliance," is often viewed as the most influential element of therapeutic effectiveness, our phenomenological study examined 14 autistic adults' experiences with anti-autistic bias in the therapeutic alliance and the relationship they perceive it has on their self-esteem. Findings, determined through thematic analysis, reveal implicit, unintentional bias was manifested through clinical assumptions about autism, explicit, overt bias was expressed through feelings of intentional harm, and repair of self-esteem was shown through positive alliances. Based on the findings of this study, we offer recommendations to help mental health practitioners and mental health practitioner training programs better serve autistic clients. This study addresses a significant gap in current research on anti-autistic bias in the mental health field and the overall well-being of autistic individuals.