Background The hundreds of thousands of patients found to have a potentially malignant pulmonary nodule each year are faced with tremendous uncertainty regarding what the nodule is and how it should be evaluated. Objective To explore patients’ responses to the detection and evaluation of a pulmonary nodule. Design Qualitative study based on four focus‐group discussions. We performed inductive analysis using principles of grounded theory to identify themes relating to responses to the nodule and strategies to manage uncertainty. Setting and participants Twenty‐two patients from two medical centres who were undergoing surveillance for an indeterminate pulmonary nodule. Results Patient responses to an indeterminate pulmonary nodule were varied and evolved over time. Although almost all patients reported an initial fear about cancer, subsequent depictions of the nodule diverged into four types defined on two dimensions: cognitive (‘it's cancer’ vs. ‘I don't know what it is’ vs. ‘it's nothing serious’) and emotional (anxiety vs. equanimity). Most eventually accepted that the nodule was unlikely to be malignant; however, some remained anxious, convinced the nodule could turn into cancer at any time and should be aggressively monitored for life. Patients used results of surveillance tests as well as their own strategies (e.g. vigilance for symptoms, information‐seeking, contemplating and controlling modifiable risk factors, avoidance, faith) to manage uncertainty. Conclusions Surveillance for a pulmonary nodule can weigh heavily on some patients for months or years. Our findings may help clinicians prepare patients with a newly detected pulmonary nodule for the burden of the prolonged uncertainty of surveillance.