OO Ser is a deeply embedded young star which brightened by 5 mag between 1994 and 1995, and gradually faded afterwards. In many respects its eruption resembled the well-known FU Orionis-type (FUor) outbursts. Since very few such events have ever been documented at infrared wavelengths, we monitored OO Ser with the Infrared Space Observatory in the 3.6-100 mum wavelength range, starting already 4 months after peak brightness and covering a period of 20 months. Eight years later, in 2004 we again observed OO Ser at 2.2 and 12 mum from the ground. The collected data provide a very unique opportunity to study the eruption of a young star at infrared wavelengths. In this contribution we present part of the data set, namely the 2.2 and 12 mum observations, from which one can reach the following conclusions: (1) the star had already returned to its pre-outburst phase by 2004, thus the timescale of its outburst was significantly shorter than that of classical FUors; (2) the fading at 12 mum was slightly faster than at 2.2-mum, somewhat contradicting to model predictions; and (3) FU Ori-type outburst models can only work for OO Ser if the viscosity parameter in the circumstellar disk, alpha, is set to an order of magnitude higher value than in other FUors.