Susan Schneider said today that Williams was struggling with depression, anxiety and the early stages of Parkinson's when he was found dead earlier this week.
The wife of the actor-comedian said he was not ready to share his Parkinson's diagnosis publicly.
Authorities have said the 63-year-old's death was suicide.
Ms Schneider did not give any details on when Williams had been diagnosed or his symptoms.
Parkinson's disease is a progressive disorder of the nervous system which affects movement. It develops gradually, sometimes starting with a small tremor in one hand. The disorder also commonly causes stiffness or slowing of movement.
Actor Michael J Fox, who has had the disease for years, is known for his efforts to fund research into it.
Ms Schneider said: "Robin's sobriety was intact and he was brave as he struggled with his own battles of depression, anxiety as well as early stages of Parkinson's disease, which he was not yet ready to share publicly."
Williams had publicly acknowledged periodic struggles with substance abuse and recently depression had prompted him to enter rehab.
Ms Schneider said those who loved Williams are taking solace in the outpouring of affection and admiration for him.
"It is our hope in the wake of Robin's tragic passing, that others will find the strength to seek the care and support they need to treat whatever battles they are facing so they may feel less afraid," she said in her statement.
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