In our practice, FDG PET-CT studies are frequently performed within days of transthoracic needle biopsy, often revealing presence of pneumothorax (PTX), a "critical finding" that should be reported expeditiously. In our experience, prevalence of PTX at PET-CT performed 1 day following biopsy is greater than 40%. Of these, approximately a third are not visible on the postprocedure chest radiography, as in a case we describe. A high level of vigilance is therefore recommended to identify PTX in patients who have undergone recent transthoracic needle biopsy, even when no PTX is present immediately following the biopsy procedure.