High intensity focused ultrasound (HIFU) can provide a means of noninvasive ablation of tissues such as tumors. However, currently the gold standard for monitoring HIFU is MRI temperature mapping. Because of the expense, lack of portability and slow update of temperature maps from MRI, ultrasonic solutions to monitoring of HIFU remain an important clinical goal. Real-time visualization of the field distribution of the HIFU source during treatment would allow the localization of the intersection of the beam with the tissue. Real-time visualization of the beam in the context of the tissue is important for proper placement of therapy especially during tissue motion. To visualize the HIFU field in a tissue, a reconstruction technique was employed using a Fourier-domain f-k migration approach with a linear array system co-aligned with the HIFU source. The reconstruction technique used the scattered signal from the medium to reconstruct the intensity field pattern of the HIFU field in situ and superimpose the intensity field image on a B-mode of the scattering medium. A 6-MHz single-element transducer (f/3) was used as the HIFU source and aligned perpendicular to the field of a linear array (L14-5) operated by a SonixRP system equipped with a Sonix-DAQ. The array had 128 elements and a measured center frequency of 6.5 MHz. The 6-MHz HIFU source was pulse excited and the fields scattered from a sample, i.e., a homogeneous tissue-mimicking phantom or a chicken breast, were received by each element of the linear array. Beam forming based on Fourier-domain f-k migration techniques were applied to the channel data to reconstruct the intensity field pattern from the HIFU source. For comparison, a wire target was placed in the field and the intensity field pattern was reconstructed by moving the wire throughout the focal region. The intensity field pattern reconstructed from the sample was compared to the field characteristics of the 6-MHz source characterized by the wire technique. The intensity field pattern was then superimposed on a registered B-mode image of the sample acquired using conventional B-mode imaging with the linear array and the SonixRP to provide context to the therapy beam placement. The beam width estimates at the HIFU focus using the in situ reconstruction technique and the wire technique were 1.7 mm and 1.5 mm, respectively. The depth of field estimates for the in situ reconstruction technique and the wire technique were 20.1 mm and 19.0 mm, respectively. Therefore, the novel reconstruction technique was able to accurately visualize the field of a focused source in the context of the interrogated medium. The visualization technique would allow real-time adjustment of the HIFU beam location in tissues during therapy.