Here we present multiwavelength observations of low-level heating in an erupting prominence observed in the UV and EUV over a wide range of temperatures and wavelengths by the Solar and Heliospheric Observatory (SOHO) Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument and the Transition Region and Coronal Explorer (TRACE), and also in Hα by the Yunnan Astronomical Observatory. The eruption occurred on 2004 April 30. The heating is relatively mild, leading only to the ionization of hydrogen and helium. It is also localized, occurring along the bottom edge of the erupting prominence and in a kinklike feature in the prominence. The heating is revealed as a decrease in the Lyman absorption relative to other parts of the prominence. This decrease results in an apparent increase in emission in all the lines observed by SUMER, especially those formed at temperatures of ~105 K. However, this is due to the disappearance of cooler absorbing material in the prominence rather than to an increase in these higher temperature species. These observations suggest that there may be low-level heating occurring in other erupting prominences that do not show heating to coronal temperatures. They also indicate that the prominence-corona transition region is best modeled with two or more structures along the line of sight. We discuss the results in terms of models of heating in erupting prominences and observations of Lyman absorption in prominences.