Sleep disorders are considered a major contributing problem in health and quality of life research but as to the date, no significant publications have appeared in this regard in Colombia. Some general considerations are discussed in the present article relevant to psychological variables affecting sleep and to the most important sleep variables that affect wakefulness and mood in the daytime. Gender, age, chronobiological and chronopyschological variables, physical, sociological and psychological status are discussed in relation to sleep disturbances. Morningness-eveningness, rigidity, vigor and personality are also taken into account as major contributing factors in the quality of sleep and wakefulness, and are regarded as important modulators of life habits and preferences in different groups. In some research papers neuroticism and negative affectivity have been found to correlate with morningness and with sleep problems, particularly in women and in advancing age; rigidity, energetic and tensional arousal must also be taken into account when appraising sleep and sleepiness problems. Finally, a recent review of the epidemiology of sleep disorders and daytime sleepiness is presented emphasizing their increasing prevalence among the very young or the elderly.