The most common complaint related to "irregular procedure"
Complaints against Scotland's eight police forces rose by 13% in the year 2008/09, figures have shown.
The total number of cases went up from 4,292 in 2007/08, to 4,862. These covered just over 8,500 allegations, up 25% on the previous year.
Grampian Police saw a 41% increase in complaints while only Strathclyde and Northern Constabulary saw a drop.
The Police Complaints Commissioner said the overall rise could partly signify greater public confident in the system.
The most common complaint allegations related to "irregular procedure", at 21%, "assault", at 18%, and "incivility", at 15%.
"Irregular procedure" complaints cover police not carrying out their duty well, such as taking a less than detailed statement or not following a particular line of inquiry.
The biggest rises were in "traffic irregularity", up 157%, "irregular procedures", up 89%, and "excessive force", up 75%.
Complaints alleging criminal behaviour also rose during the year to March 2009, from 839 to 1,025, but only led to proceedings being taken in seven cases.
Police Complaints Commissioner for Scotland John McNeill said complaints were part of policing, but that the figures provided lessons to improve the way forces work.
"The collection and analysis of complaints is fundamental to the culture of continuous improvement that I want to encourage in Scotland's police," he added.
"I would argue that any increase in complaints arises in part from the public having more confidence in the police and expecting higher standards from them.
"When they feel let down, they are making use of the formal complaints systems that exist to register that dissatisfaction."
The Association of Chief Police Officers in Scotland said it would study any lessons which emerged from the figures and welcomed the comments from the commissioner on a rising confidence in the public over making complaints.
A spokesman said: "Whilst there are complaints about the police, it should always be remembered that when this is measured against the number of times officers interact and have contact with the public, overall the police in Scotland operate in a highly professional manner and officers should be praised for the quality of service they deliver, often in difficult circumstances."
Meanwhile, Liberal Democrat justice spokesman Robert Brown said it was alarming excessive force complaints rose 75%.
"Whilst not all of these complaints will be justified, that there has been such a significant rise in serious complaints surely merits close examination," he said.