The hospitalizations are part of cancer care and has been studied by researchers worldwide. A better understanding about their associated factors may help to achieve improvements on this area. The aims of this study were to investigate the association between demographic and clinical characteristics and hospitalizations, as well as between these characteristics and the length of stay (LOS), within the first year of outpatient treatment, for the most incident cancers in the Brazilian population. In this cohort study, we investigated 417,477 patients aged 19 years or more, who started outpatient cancer treatment, from 2010-2014, for breast, prostate, colorectal, cervix, lung and stomach cancers. The outcomes evaluated were: i) Hospitalizations within the first year of outpatient cancer treatment; and ii) LOS of the hospitalized patients. It was performed a binary logistic regression to evaluate the association between the explanatory variables and the hospitalizations and a negative binomial regression to evaluate their influence on the length of hospital stay. The hospitalizations occurred for 34% of patients, with a median of LOS of 6 days (IQR: 2-15). Female patients were 16% less likely to be hospitalized (OR: 0.84; 95% CI: 0.82-0.86), with lower average of LOS (AR: 0.98; 95% CI: 0.97-0.99), each additional year of age reduced in 2% the hospitalization odds (OR: 0.98; 95% CI: 0.98-0.99) and in 1% the average of LOS (AR: 0.99; 95% CI: 0.98-0.99), patients from South region had twice more chances of hospitalization than from North region (OR: 2.01; 95% CI: 1.93-2.10) and patients with colorectal cancer had greater probability of hospitalization (OR: 4.42; 95% CI: 4.27-4.48), with the highest average of LOS (AR: 1.37; 95% CI: 1.35-1.40). In view of our results, we consider that the government must expand the policies with potential to reduce the number of hospitalizations.