Health chiefs in the Western Isles drafted in the consultant psychiatrist who spent 40 hours on duty and the rest of the time on call.
The £19,305.22 fee paid was revealed after a freedom of information request to the health board.
It said agency staff are only used when there are no other options to provide cover and “high” costs can be incurred when a gap has to be filled urgently.
NHS Western Isles’ spending on temporary consultants increased from £452,000 in 2012 to £1.2 million last year, according to reports, while the number of consultants employed dropped from 43 to 36 over the same period.
The £19,000 paid to the consultant specialising in old age care included VAT and a fee to the agency.
A spokeswoman for NHS Western Isles said: “During a period of extended sickness absence in 2013, a consultant psychiatrist was hired from an agency to cover one week’s annual leave for the remaining consultant.
“The locum consultant undertook 40 normal working hours and provided 128 hours on call for which the cost to the board was £19,305.22. This figure is the gross total paid to the agency and includes 20 per cent VAT.
“NHS Western Isles’ spending on temporary agency consultants rose from £452,000 in 2012 to £1.2 million in 2014.
“The number of temporary agency consultants hired decreased from 43 in 2012 to 36 in 2014, but it is important to bear in mind that the duration of locum placements varies considerably.”
Health Secretary Shona Robison said: “We have a record number of consultants working in Scotland’s NHS and boards are working hard to recruit even more. Workforce in the Western Isles is up 3 per cent under this government.
“When the use of agency staff is required, we have long-standing framework contracts in place which allow us to engage staff at nationally agreed rates of pay.
“These contracts are reviewed on a regular basis to ensure they continue to meet the needs of NHS Scotland and health boards have been advised to only use agencies that are on the nationally agree contract.
“We have also established a national supplementary staffing group which will look at the use of all temporary staff and seek to make recommendations on how we can reduce it.”