Travail reçu le 24 février 2005 et accepté le 24 mai 2006. Tirés à part : R. Courtois (à l'adresse ci-dessus). Links between stress factors, mental health and initial consumption of tobacco and alcohol during pre-adolescence Summary. Background-We know the effects of stress hassles and life events on mental health at pre-adolescence and the impact of the first experiences with alcoholic beverages and tobacco, where the precocity of the initiation tends to encourage abuse and later dependence on these substances. The goal of this study was to look into the related effect of environmental factors (daily hassles, life events, and social support) on perceived mental health and on the initiation and consumption of tobacco and alcohol by preadolescents. Methods-Population-The study was carried out in 12 institutions in a French department (« Indre-et-Loire ») in the « Région Centre », including students from the last year of primary school (fifth grade) and the first two years of middle school (sixth and seventh grades) : all nine elementary schools in Joué-lès-Tours, the second largest city of the department, and three middle schools in Tours and surrounding areas (urban, semi-rural and inner city). The sample was made up of 476 preadolescents attending school, 234 girls (49 %) and 242 boys (51 %), 267 primary school and 209 middle school students, with an average age of 11 years and 7 months. Material-Standardized questionnaires, specific to this population : with a scale of daily hassles (10, 35, 36) , life events (8, 41) , mental health (7, 35, 42) , and social support (8, 44) , were used. They proved to be adapted to each of them (Cronbach alpha coefficient > 0.70) and the types of hassles and life events corresponded to the psycho developmental knowledge specific of this period. For the middle school students, dependence on tobacco was defined according to the « Hooked on nicotine checklist » (18, 33). Procedure-In April 2004 in class (anonymity guaranteed). Results-The results show that the hassles (considered in terms of occurrence or intensity, that is, the perceived stress) and life events (occurrence and negative perception) have a negative effect on mental health. In particular, pressure due to family problems has the greatest influence on mental health. For primary school students, this is followed by problems linked to self-perception ; for middle school students, those linked to school. The consequences of hassles and life events on mental health allowed us to verify the solidity of the model used in previous studies [the Lausanne pediatric psychiatry team (11, 35) ], even with a younger preadolescent population. The effect of daily hassles is greater than that of life events, but they are not independent of one another (mediational model). Social support plays a modulating and protective role in mental health and the effects of daily hassles and life events. The prevalence of preadolescent smokers (simple experimentation or more or less regular use) is 5.7 % (n = 26). The prevalence of alcohol use is greater, encompassing more than one-third of subjects (33.4 % ; n = 153). The influence of daily hassles can be seen both on the age of initiation to alcoholic beverages and to use of alcohol and intoxications. It is also observed on the age of initiation to tobacco and nicotine dependence (only taken into account for middle school students). That is to say that they promote precocity in the consumption of these products and increase their use. The absence of links with tobacco consumption may be due to the low number of preadolescent tobacco users. Life events also show an effect on tobacco and alcohol consumption, but L'Encéphale, 2007 ; 33 : 300-9, cahier 1 Liens entre stresseurs, santé psychique et premières consommations de tabac et d'alcool 301 Résumé. L'objectif de ce travail est d'étudier l'effet relatif de facteurs environnementaux (tracas quotidiens, événements de vie et support social) sur la santé psychique perçue, et les consommations tabagiques et de boissons alcoolisées chez des préadolescents (notamment les premières expérimenta-tions). La population est composée d'élèves de fin d'école pri-maire et de début de collège : CM2, 6 e et 5 e (N = 476 sujets, 49 % de filles et 51 % de garçons, âge moyen de 11,7 mois, ET = 0,79). Des questionnaires standardisés, spécifiques à cette période de vie (échelle de tracas, d'événements de vie, de santé psychique, de support social) ont été utilisés. Ils se sont avérés adaptés pour chacun d'entre eux (coefficient alpha de Cronbach > 0,70) et les types de tracas et d'événe-ments de vie (EDV) sont en correspondance avec les con-naissances psychodéveloppementales propres à cette période. Les résultats montrent que les tracas et les EDV ont un effet négatif sur la santé psychique ; l'effet des tracas est plus important que celui des événements de vie, mais ils ne sont pas indépendants l'un de l'autre (modèle médiationnel). Le support social joue un rôle modulateur sur la santé psy-chique et sur les effets des tracas et événements de vie. La plupart de ces liens (notamment l'effet des tracas) ont été retrouvés pour les premières expérimentations, l'usage de tabac et de boissons alcoolisées, les ivresses et la dépen-dance tabagique. Seul le rôle éventuellement protecteur du support social n'a pu être mis en évidence.