CriticismThe extensive scientific studies of George Bonanno show that the Kübler-Ross stages of grief are, as Kübler-Ross herself explained, variable in extent and detail, and the entire process is not always completed. In Bonanno's book, "The Other Side of Sadness: What the New Science of Bereavement Tells Us About Life After a Loss," he summarizes his rigorously peer-reviewed research based on thousands of subjects and conducted over more than two decades. His findings include that a natural resilience is the main component of grief and trauma reactions. The logic is that if there is no grief, there are no stages to pass through. Bonanno's work has also demonstrated that absence of grief or trauma symptoms is a healthy outcome, rather than something to be feared as has been the thought and practice until his research.

A 2000–2003 study of bereaved individuals conducted by Yale University obtained some findings that were consistent with the five-stage theory and others that were inconsistent with it. Several letters were also published in the same journal criticizing this research and arguing against the stage idea. Skeptic Magazine published the findings of the Grief Recovery Institute, which contested the concept of stages of grief as they relate to people who are dealing with the deaths of people important to them.