This study aims to clarify the surgical treatment time of pulmonary metastasis in patients with colorectal cancer.Early relapse after resection of pulmonary metastasis is often encountered when the interval from the detection of pulmonary metastasis to pulmonary metastasectomy was short.In this retrospective analysis, data of patients with colorectal cancer who underwent surgical treatment of pulmonary metastasis at the Gunma Prefectural Cancer Center, Gunma, from April 2001 through September 2018 were evaluated. The patients were divided into 2 groups. We examined the interval period from the diagnosis of pulmonary metastasis to pulmonary metastasectomy. This period was divided into every 3 months, and the prognosis of each group was compared with clarify the appropriate timing of pulmonary metastasectomy.The primary endpoints were 5-year overall survival and recurrence-free survival rates.The most significant difference was observed when the cutoff value was 9 months (5-year recurrence-free survival 45.8% vs 85.6%, P < .01). No significant difference was found in any background factors between the 2 groups. Twenty-five patients (34.7%) experienced recurrence after pulmonary metastasectomy. The most common site of recurrence was the lung (48%). Among the 12 cases of recurrence of pulmonary metastasis, 11 cases belonged to the <9 months group. A multivariable survival analysis found that the interval period of <9 months was a significant predictor of recurrence.Our study suggests that clinical follow-up for 9 months prior pulmonary metastasectomy in colorectal patients would improve the prognosis.