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Background and Objective: There are some factors including socio-demographic, maternal and nutritional variables reported to influence the growth of children in the first two years of life. The aim of this study was to determine some factors related to undesirable growth of 6 months–2years old children in Tabriz-Iran. Materials and Methods: In this case - control study 233 children with undesirable growth as cases, and 412 children with desirable growth as controls selected in five primary health care centers in Tabriz city in North-West of Iran during 2007. A questionnaire which included some questions regarding demographic characteristics, fertility history, and nutritional status was filled by using face -to - face interview with selected children’s mother. The influence of different factors on undesirable growth was evaluated with a logistic regression model by using SPSS-14 and EPI-2000 software. Results: Having any disease during two monitoring (OR=4.23, 95% CI: 2.95-6.07, P<0.001), type of pregnancy (unwanted) (OR=1.87, 95% CI: 1.20-2.93, P<0.006), gender (girl) (OR=1.51, 95%CI: 1.05-2.17, P<0.025), low birth weight (OR=1.0, 95% CI: 0.99-1.01, P<0.097) and having conflict in the family (OR=1.22, 95% CI: 1.01-1.47, P<0.045) associated with undesirable growth. Conclusion: This study determined having any disease, type of pregnancy, sex of child and low birth weight related with undesirable growth of 6 months –2years old children. Using safe family planning methods and help to reduce unwanted pregnancy, parental training about the nutritional requirements of children particularly during period of disease, is recommended in order to enhance the health of children.