A generalization of a growth model with endogenous fertility Massimiliano Ferrara and Luca Guerrini Abstract. In this paper, we study the equilibrium dynamics of an en- dogenous growth model with endogenous fertility choice. In this setting, we show that there is a unique equilibrium which is globally determinated. The validity of the neo-Malthusian relation between fertility and growth is then examined. M.S.C. 2000: 49Q99, 91B62. Key words: endogenous growth, endogenous fertility, BGP equilibrium. 1 Introduction This paper focuses on the equilibrium dynamics of an endogenous growth model with physical capital in which fertility enters the utility function. Our model is an extension of the work of Yip and Zhang [11], who carried out a study to provide a reconciliation for the conflicting findings in the literature on the relationship between population growth and economic growth. Some works in fact suggested that high fertility suppressed per capita income growth, others instead expressed ambivalence about this neo-Malthusian relationship (see, e.g., Blanchet [3], Coale and Hoover [4], Kelley [6], Simon [9], Srinivasan [10]). In our endogenous growth framework, we follow the existing literature by allowing the number of children to enter the utility function (see, e.g., Barro and Becker [2], Palivos [7], Yip and Zhang [12]). The presence of fertility implies that the budget constraint is no longer convex, and so an extra condition has to be imposed to guarantee the sufficiency of the necessary conditions for an optimum. By assuming that the marginal product of capital minus the population growth rate is monotonically decreasing with respect to capital, and the elasticity of the marginal productivity of labor is less than one, we find that there is only one balanced growth path (BGP) equilibrium. Moreover, we examine the relationship between fertility growth and economic growth along a BGP equilibrium, and see that there exists a negative relationship between them only when all exogenous factors are controlled for. This suggests that the conflicting findings in the literature between population growth and economic growth may be originate from heterogeneity in unobserved variables across countries and over time in cross-country panel data sets. Differential Geometry - Dynamical Systems, Vol.8, 2006, pp. 98-104. c  Balkan Society of Geometers, Geometry Balkan Press 2006.