Abstract: Learning that a child has a lifelong developmental disorder is stressful and challenging to any family, yet it is clear that some families adapt and adjust more readily than others. In this article, it is proposed that a diagnosis of an autism spectrum disorder (ASD) is especially likely to be experienced as ambiguous loss. Interviews with mothers of children with ASDs are used to identify whether mothers express feelings of ambiguous loss when talking about their child. Then, a specific hypothesis derived from ambiguous loss theory—that higher levels of identity ambiguity in mothers are linked to higher levels of depressive symptoms and perceived stress independent of the severity of the child’s diagnosis—is tested and found to be supported. Recognition of ambiguous loss in families of children with ASDs would help professionals provide more effective support and assistance to families.