The Hutt Valley District Health Board has been criticised for the second time in a week over the care given to a patient with mental health problems.
The case was detailed in a report released by the Health and Disability Commissioner on Tuesday.
Anthony Hill says the DHB allowed a woman's intellectual impairment to overshadow her other problems.
Mr Hill says the woman lived at home but wanted to leave. She was seen often by police, the hospital and the DHB Crisis Assessment and Treatment team between 2007 and 2010, but most put her self-harm, suicide threats and troubled behaviour down to her intellectual impairment.
The woman was found dead in 2010 after being returned home by police, and running away again.
Mr Hill says health workers allowed the woman's intellectual impairment to over-shadow her worsening mental health problems. He says many agencies were involved in her care and communication between the different providers was limited.
Mr Hill believes the Hutt Valley District Health Board should have taken charge and realised that fuller assessment and diagnosis was needed.
"This woman had intellectual impairment and had mental illness. And I think there was a tendency to allow the behaviours to be attributed to the intellectual impairment, without properly exploring the possibility of mental illness.
"Consequently, the appropriate diagnosis and assessment wasn't undertaken."
Last week, the DHB said it had improved mental health services following a critical inquiry done for the Ministry of Health concerning 2008 to 2010.