Two-thirds of those who died by suicide had a history of self-harm, but of those 35% had not been seen or treated following the previous episode.
A new study, which analysed 307 suicides in the Cork area over a five-year period built up profiles of those who had died and found that in 162 cases, there was no documentation as to whether or not the deceased had a mental health diagnosis.
The study, conducted by the National Suicide Research Foundation and published in the journal Social Psychiatry and Psychiatric Epidemiology found that in the 145 cases where there was information on mental health, illnesses included depression, anxiety and schizophrenia.
Data were collected between September 2008 and December 2012 on individuals who had died by suicide from May 2007 to June 2012.
Most were Irish, the median age was 39 and the study said there was, at 80%, a "significant over-representation" of males in the sample.
For 132 cases, information was available on self-harm history and 86 individuals (65.2%) had engaged in at least one episode of previous self-harm.
It also showed that 10.5% had engaged in self-harm less than one week prior to suicide, 14% less than one month, and 26.7% in the 12 months or longer prior to suicide.
According to the study, of the 86 people with a known history of self-harm, in 52 cases, information was available on medical treatment following the most recent episode of self-harm and of those 52 cases, 27 (51.9%) had presented to a general hospital and seven (13.5%) had received treatment from a general practitioner (GP).
"However, 18 (34.6%) had not received any medical treatment after their most recent episode of self-harm," it said.
"More than one-third of suicide cases had not received any medical treatment after the most recent episode of self-harm, while more than half had not received any treatment after the most recent episode of self-harm.
"This highlights potential for increased efforts to ensure that appropriate treatment is received after incidents of self-harm."
In the 121 cases where there was information on whether the deceased had ever received inpatient mental health treatment, 43% had been admitted to a mental health ward at least once.
For 91 cases where there was information available on GP visits in the past year, almost 20% had attended once, 16.5% had attended between two and four times, 44% had attended more than four times, and the remainder had not attended in the past year.
According to the authors, who included Daniel Leahy, Celine Larkin and Dr Ella Arensman: "More than one-third of suicide cases had not received any treatment after previous self-harm, but the majority had visited their GP on more than one occasion in the past year.
"This finding underlines the previous research showing low rates of recently seeking help among people who died by suicide.
"Earlier studies have emphasised the importance of recognising at-risk individuals in the community and primary care settings, and ensuring that appropriate treatment is provided."
In 162 cases, there was no documentation as to whether or not the deceased had a mental health diagnosis.
In the 145 cases where there was information on mental health, illnesses included depression, anxiety and schizophrenia.