The Collaborative International Dictionary of English v.0.48:

Somnambulation \Som*nam`bu*la"tion\, n. [L. somnus sleep +
   ambulatio a walking about, from ambulare to walk. See
   Somnolent, Amble.]
   The act of walking in sleep, called also sleepwalking.
   [1913 Webster]

WordNet (r) 3.0 (2006):

somnambulation
    n 1: walking by a person who is asleep [syn: sleepwalking,
         somnambulism, somnambulation, noctambulism,
         noctambulation]