  The EGRET source 3EG J1835+5918 is the brightest and most accurately
positioned of the as-yet unidentified high-energy gamma-ray sources at high
Galactic latitude (l,b=89,25). We present a multiwavelength study of the region
around it, including X-ray, radio, and optical imaging surveys, as well as
optical spectroscopic classification of most of the active objects in this
area. The identified X-ray sources in or near the EGRET error ellipse are
radio-quiet QSOs, a galaxy cluster, and coronal emitting stars. The radio
sources inside the error ellipse are all fainter than 4 mJy at 1.4 GHz. In
addition there are no flat-spectrum radio sources in the vicinity. Since no
blazar-like or pulsar-like candidate has been found as a result of these
searches, 3EG J1835+5918 must be lacking one or more of the physically
essential attributes of these known classes of gamma-ray emitters. If it is an
AGN it lacks the beamed radio emission of blazars by at least a factor of 100
relative to identified EGRET blazars. If it is an isolated neutron star, it
lacks the steady thermal X-rays from a cooling surface and the magnetospheric
non-thermal X-ray emission that is characteristic of all EGRET pulsars. If a
pulsar, 3EG J1835+5918 must be either older or more distant than Geminga, and
probably an even more efficient or beamed gamma-ray engine.
