Different states have different rules. This tip deals only with Oregon law.
If you have ever been arrested or convicted of a crime, you may be able to get the record set aside – or expunged. The first thing you should do is to contact an attorney in the state where you were arrested/convicted. (This is an area, however, where a diligent do-it-yourselfer may get by without an attorney in many, but not all, situations.) The attorney will file a Motion to Set Aside Conviction and/or Arrest. The motion must be filed with the court in the county where you were arrested/convicted, along with a copy of your fingerprints if you are setting aside a conviction. Expunction does not happen automatically after the passage of a certain amount of time; a motion needs to be filed.
Not all crimes can be expunged. Generally, traffic crime (such as DUII) convictions cannot be expunged (but traffic crime arrests can be). Class A felonies cannot be expunged. With few exceptions such as Criminally Negligent Homicide (ORS 163.145), Class B felonies cannot be expunged either. Most all Class C felonies and most all misdemeanors can be expunged. ORS 137.225, the Oregon law on the subject, lists crimes that are the exceptions to these general rules.
If you are setting aside an arrest that did not lead to charges being brought, you must wait until one year after the date of the arrest. If charges were brought against you but later dismissed, you may immediately move to have the arrest set aside.
If you are setting aside a conviction, three years must have passed since the date of conviction. Whether setting aside a conviction or an arrest, you must not have any criminal charges pending and you must not have had a second criminal conviction within the preceding 10 years from the date of filing your motion to set aside the conviction or arrest. If you are only moving to set aside a record of arrest, in addition to having no convictions in the preceding 10 year period you also must have had no other arrests within a 3 year period prior to filing. Most often, the court will grant your motion to set aside the arrest/conviction without requiring a court appearance. Once the court grants your motion, it takes a few weeks for your record or arrest/conviction to be removed from the various databases.