Fluoxetine (FIx) is cunently one the most commonly prescribed antidepressant medications for adolescents suffering from various emotional disorders. FIx has been approved by the United States Food and Drug Administration (FDA) for the treatment of adolescent major depressive disorder (MDD) and obsessive compulsive disorder (OeD), despite limited research into the possible long-term effects of this psychoactive substance on the developing adolescent brain. The cunent study aimed to investigate the effects of adolescent FIx exposure on later anxietylike behaviour in rats. The current study involved the oral administration of FIx hydrochloride, via drinking water, to Inale and female adolescent PVG/C Hooded rats. There were three treatment conditions with differing FIx treatment periods (early, late or early plus late), and a control group. Immediately following FIx treatment, all groups were tested on an acute open-field test. The rats were then tested on two later occasions during adulthood on a battery of anxiety-related tests: the light-dark box test, the responsiveness to brightness change Y -maze and the social interaction test (SIT). On the acute open-field test, the FIx-treated rats displayed greater ambulation and possibly lower corner square occupancy, suggestive of an acute anxiolytic effect of FIx. The chronic effects testing suggested that rats treated during the late phase of adolescence, either alone or in combination with early treatlnent, were the Inost affected by FIx. The late FIx-treated group spent less time in the light during the light-dark box test, and defecated more than other groups during the SIT. In addition, the males within the late FIx-treated group spent significantly more time within the comer squares and less time within the centre squares of the SIT apparatus than males from the early FIx-treated group. Overall this study suggests that the long-term effects of adolescent FIx use are anxiogenic.