Night eating syndrome (NES) is a rather common problem and may be one of the more frequent causes of obesity. It is not an "official" type of eating disorder yet. But experts think that about 1-2 percent of the general population have severe impairments caused by night food craving. More than 5 percent of the patients seeking therapy for obesity report symptoms of this syndrome. It is much more than just a bad habit, but a more severe problem for affected patients. NES is a stress-related eating, sleeping and mood disorder that is associated with disordered neuroendocrine function. It follows a characteristic circadian pattern and has responded to an agent that enhances serotonin function.Therapy should be a combination of psychotherapy and medication.

Cognitive behaviour therapy may help to identify the typical triggers and possible alternatives for this behaviour. Writing an eating diary may be a good way to improve awareness and control over the syndrome. According to a recent article antidepressant medication with an SSRI (sertraline) may be a good pharmacological treatment. Here is the Medline abstract of the article :
Clinical trial of sertraline in the treatment of night eating syndrome.
O'Reardon JP, Stunkard AJ, Allison KC.
Int J Eat Disord. 2004 Jan;35(1):16-26.

OBJECTIVE: To test the efficacy of sertraline in the treatment of night eating syndrome. METHODS: Seventeen patients meeting criteria for night eating syndrome received sertraline in a 12-week open-label, nonblind trial. Outcome was assessed by four primary measures, namely, the number of nocturnal awakenings, the number of ingestions, total daily caloric intake after the evening meal, and an overall rating of change from the Clinical Global Impression of Improvement scale (CGI-I). RESULTS AND DISCUSSION: An intent-to-treat analysis revealed highly significant improvements across all four primary outcome measures for all 17 subjects. Five subjects achieved full remission of symptoms (CGI-I score of 1 = very much improved) and lost a significant amount of weight over the course of the study (-4.8 +/- 2.6 kg, p < .05). Sertraline, a selective serotonin reuptake inhibitor, may be beneficial in the treatment of night eating syndrome.