Objectives: The goal of this study was to identify chronic conditions and multimorbidity patterns in patients with coronavirus disease 2019 (COVID-19) and to examine their associations with pneumonia and death. Methods: This cross-sectional study analyzed the official data of COVID-19 patients in Mexico through May 18, 2020 (released by the Secretaría de Salud de México). Adjusted logistic regression models were applied to assess the associations of comorbidities with pneumonia and death. The marginal effects were estimated, and the probability of pneumonia or death according to the number of comorbidities was graphed for each year of age. Results: Of the 51 053 COVID-19 patients enrolled in the final analysis, 27 667 (54.2%) had no chronic conditions, while 13 652 (26.7%), 6518 (12.8%) and 3216 (6.3%) were reported to have 1, 2, and 3 or more simultaneous conditions, respectively. Overall, a significant incremental gradient was observed for the association between multimorbidity and pneumonia (p<0.001); for 2 chronic conditions, the adjusted odds ratio (aOR) was 2.07 (95% confidence interval [CI], 1.95 to 2.20), and for ≥3 conditions, the aOR was 2.40 (95% CI, 2.22 to 2.60). A significant incremental gradient was also found for the relationship between multimorbidity and death (p<0.001); an aOR of 2.51 (95% CI, 2.30 to 2.73) was found for 2 chronic conditions and an aOR of 3.49 (95% CI, 3.15 to 3.86) for ≥3 conditions. Conclusions Underlying chronic conditions and multimorbidity are associated with pneumonia and death in Mexican COVID-19 patients. Future investigation is necessary to clarify the pathophysiological processes behind this association, given the high burden of chronic diseases in various countries, including Mexico.