As they say, religious belief or more precisely faith, is the belief in things absent any evidence and thus reason for that belief. Sounds like delusion to me.
In clinical practice, no clear guidelines exist to distinguish between "normal" religious beliefs and "pathological" religious delusions. Historically, psychiatrists such as Freud have suggested that all religious beliefs are delusional, while the current DSM-IV definition of delusion exempts religious doctrine from pathology altogether. From an individual standpoint, a dimensional approach to delusional thinking (emphasizing conviction, preoccupation, and extension rather than content) may be useful in examining what is and is not pathological. When beliefs are shared by others, the idiosyncratic can become normalized. Therefore, recognition of social dynamics and the possibility of entire delusional subcultures is necessary in the assessment of group beliefs. Religious beliefs and delusions alike can arise from neurologic lesions and anomalous experiences, suggesting that at least some religious beliefs can be pathological. Religious beliefs exist outside of the scientific domain; therefore they can be easily labeled delusional from a rational perspective. However, a religious belief's dimensional characteristics, its cultural influences, and its impact on functioning may be more important considerations in clinical practice."
"American Psychological Association To Classify Belief in God As a Mental Illness"
About time too.