The term «loss» in this article refers to the lack of a significant adaptive resource that is a central part of the affective world of the subject. The absence of such resource can generate psychological distress. Old age is seen as a time in which numerous changes occur that are associated with losses in important areas of life and which, as a whole, constitute a major source of stress. These losses involve a series of physical, social and psychological changes that affect and define old age and that require the subject to develop a process of adaptation to many intense stressors. Loss structure can be defined as a set of significant objects (that can be grouped under different loss categories), perceived as being under threat of being lost, effectively lost, or whose existence is uncertain or ambiguous (conceived of as types of loss), and whose influence continues to define cognitions, affection and behaviors. The unprecedented loss structure found in elderly adults could set up different routes of maladjustment. Maladjustment appear in three fundamental areas: psychological, physical and social. Hence, frustration can lead to depression. Successive losses seen as a series of failures can generate feelings of despair; losses related to sources of affection can produce loneliness, etc. The Loss Structure Scale (LSS), proposed here is an instrument for exploring losses that usually occur in old age. It also allows a systematic exploration of a wide range of losses previously validated in the Mexican context as a first approach to possible psychosocial causes of psychological maladjustment in old age. Method The project was divided into two phases. The first corresponded to the design of the LSS, and the second to a psychometric evaluation. Four samples were used with subjects chosen by availability in Mexico City. One model of the scale was explored that consisted of 60 items linked to experiences of loss with three reply options for each item: No loss, Ambiguous loss, and Definite loss in a final sample of 193 subjects (69.34% women, N = 134). The following instruments were used: The Center of Epidemiological Studies Depression Scale; Beck's Anxiety Inventory; Hunter Opinions and Personal Expectations Scale; the perceived disease subscale of WHOQoL- Brief; The World Health Organization Quality of Life Assessment, Brief; the Lack of Emotional Wellbeing subscale of the Multifaceted Loneliness Inventory and the Anxiety About Aging Scale. Results Factor structure. A factor analysis was carried out using the principal components method with varimax rotation and eigen values greater than one. The final factor structure showed nine well defined factors covering 36 items with an internal alpha consistence of .91 explaining 67.4% of the variance. Alpha values for the internal consistence of the 9 factors fluctuated between .74 and .83. Construct validity. 1) Moderately high correlations were obtained between total score on the Loss Structure Scale and all psychological maladjustment variables (between r=.50 and r=.66; p<.01), with the exception of aging anxiety, which seems to point to the important pathogenic role of losses suffered in most of the maladjustment variables, 2) a negative association was found between the frequency of no losses and the afore mentioned variables, with depression (r=-.70, p<.01) and loneliness (r=-.68, p<.01), 3) ambiguous loss frequency correlated positively with depression (r=.54, p<.01), loneliness (r=.47, p<.01), anxiety (r=.42, p<.01) and aging anxiety (r=.40, p<.01), 4) the frequency of definite losses correlated strongly with loneliness (r=.53, p<.01), depression (r=.50, p<.01) and perceived disease (r=.47, p<.01).… [ABSTRACT FROM AUTHOR]