Leaf area index (LAI) is a useful variable to characterize crop dynamics, productivity and water requirements. The three-fold aim of this work was to estimate the LAI of poplano pepper (Capsicum annuum L.) with a ceptometer, compare the results with the destructive method and analyze the relationship between the LAI and crop yield. The experiment was carried out in a greenhouse at the Colegio de Postgraduados, Montecillo campus. The transplant date was April 21 and the harvest ended on November 11, 2014. Tezontle was used as substrate and drip irrigation was applied. The experiment consisted of three treatments (T): T1 (two stems), T2 (three stems) and T3 (without pruning). To estimate the LAI, a ceptometer was used to measure the radiation intercepted above and below the canopy. Leaf area was measured with the LI-3100C area meter. Results indicated that the maximum LAI occurred at flowering, corresponding to 2,096 growing degree days (GDD) with 0.93, 1.2 and 2.75 for T1, T2 and T3. Estimating LAI with a ceptometer proved to be a suitable and reliable method, since the linear correlation coefficient (R2) obtained between the two methods was 0.82, 0.94 and 0.99, for T1, T2 and T3, respectively. The yield obtained was 10.74, 8.28 and 5.49 kg∙m-2 for T3, T2 and T1, respectively. Increasing the number of stems per plant increased LAI, yield and number of fruits; however, fruit size decreased.